Help the eccentric professor complete his rather alarming report to the safety committee.
The highly explosive chemical compound _____ yesterday has mysteriously vanished from the laboratory.
The correct answer is with which I was experimenting.
The verb phrase is "experiment with." In formal writing, we shift the preposition to the beginning of the relative clause ("with which").
Watch out for the sneaky double preposition trap! If you move "with" to the front, you cannot leave another "with" at the end of the clause.
Relative Clause
A relative clause is a kind of subordinate clause that contains the element whose interpretation is provided by an antecedent on which the subordinate clause is grammatically dependent; that is, there is an anaphoric relation between the relativized element in the relative clause and antecedent on which it depends.
Typically, a relative clause modifies a noun or noun phrase, and uses some grammatical device to indicate that one of the arguments within the relative clause has the same referent as that noun or noun phrase. For example, in the sentence *I met a man who wasn't there*, the subordinate clause who wasn't there is a relative clause, since it modifies the noun man, and uses the pronoun who to indicate that the same "man" is referred to within the subordinate clause (in this case, as its subject).
In many European languages, relative clauses are introduced by a special class of pronouns called relative pronouns, such as who in the example just given.
Restrictive and Non-restrictive
Bound relative clauses may or may not be restrictive. Whereas a non-restrictive or non-defining relative clause merely provides supplementary information, a restrictive or defining relative clause modifies the meaning of its head word (restricts its possible referent).
For example:
- *The man who lives in this house has not been seen for days*. This (*who lives in this house*) is a restrictive relative clause, modifying the meaning of man, and essential to the sentence (if the clause were omitted, it would no longer be known which man is being referred to). If the bold part is deleted the remaining part does not provide the sense.
- The mayor, who lives in this house, has not been seen for days. This is a non-restrictive relative clause, since it provides supplementary information about the mayor, but is not essential to the sentence – if the clause were omitted, it would still be known which mayor is meant. If the bold part is deleted the remaining part provides the sense. In speaking it is natural to make slight pauses around non-restrictive clauses, and in English this is shown in writing by commas (as in the examples).
Another difference in English is that only restrictive relative clauses may be introduced with that or use the "zero" relative pronoun. In colloquial speech, a non-restrictive relative clause may have a whole sentence as its antecedent rather than a specific noun phrase; for example:
- *The cat was allowed on the bed, which annoyed the dog*.
Here, the context of the sentence (presumably) indicates that which refers not to the bed or the cat but to the entire proposition expressed in the main clause, namely the circumstance that the cat was allowed on the bed. Such constructions are discouraged in formal usage and in texts written for nonnative speakers because of the potential for ambiguity in parsing; a construction more accepted in formal usage would be The cat's being [or having been] allowed on the bed annoyed the dog.
Finite and Non-Finite
Relative clauses may be either finite clauses (as in the examples above) or non-finite clauses. An example of a non-finite relative clause in English is the infinitive clause on whom to rely, in the sentence "She is the person on whom to rely".
Relative Clauses in English
In English, a relative clause follows the noun it modifies. It is generally indicated by a relative pronoun at the start of the clause, although sometimes simply by word order. If the relative pronoun is the object of the verb in the relative clause, it comes at the beginning of the clause even though it would come at the end of an independent clause ("He is the man whom I saw", not "He is the man I saw whom"). The choice of relative pronoun can be affected by whether the clause modifies a human or non-human noun, by whether the clause is restrictive or not, and by the role (subject, direct object, or the like) of the relative pronoun in the relative clause.
- For a human antecedent, "who", "whom", or "that" is usually used ("He is the person who saw me", "He is the person whom I saw", "He is the person that I saw"). For a non-human antecedent, only "that" or "which" is used.
- For a non-human antecedent in a non-restrictive clause, only "which" is used ("The tree, which fell, is over there"); while either "which" or "that" may be used in a restrictive clause ("The tree which fell is over there", "The tree that fell is over there")—but some styles and prescriptive grammars require the use of "that" in the restrictive context.
- Of the relative pronoun pair "who" and "whom", the subjective case form ("who") is used if it is the subject of the relative clause ("He is the policeman who saw me"); and, in formal usage, the objective case form ("whom") if it is the object of the verb or preposition in the relative clause ("He is the policeman whom I saw", "He is the policeman whom I talked to", "He is the policeman to whom I talked"); but in informal usage "whom" is often replaced by "who".
In English, non-restrictive relative clauses are set off with commas, but restrictive ones are not:
- "I met a man and a woman yesterday. The woman, who had a thick French accent, was very pretty." (non-restrictive—does not narrow down who is being talked about)
- "I met two women yesterday, one with a thick French accent and one with a mild Italian one. The woman who had the thick French accent was very pretty." (restrictive—adds information about who is being referred to)The status of "that" as a relative pronoun is not universally agreed.
Preposition
Prepositions form a closed word class, although there are also certain phrases that serve as prepositions, such as in front of.
A single preposition may have a variety of meanings, often including temporal, spatial and abstract. Many words that are prepositions can also serve as adverbs. Examples of common English prepositions (including phrasal instances) are of, in, on, over, under, to, from, with, in front of, behind, opposite, by, before, after, during, through, in spite of or despite, between, among, etc.
A preposition is usually used with a noun phrase as its complement.
A preposition together with its complement is called a prepositional phrase.
Examples are in England, under the table, after six pleasant weeks, between the land and the sea.
A prepositional phrase can be used as a complement or post-modifier of a noun in a noun phrase, as in the man in the car, the start of the fight; as a complement of a verb or adjective, as in deal with the problem, proud of oneself; or generally as an adverb phrase.
English allows the use of "stranded" prepositions. This can occur in interrogative and relative clauses, where the interrogative or relative pronoun that is the preposition's complement is moved to the start (fronted), leaving the preposition in place. This kind of structure is avoided in some kinds of formal English.
For example:
- What are you talking about? (Possible alternative version: About what are you talking?)
- The song that you were listening to ... (more formal: The song to which you were listening ...)
Notice that in the second example the relative pronoun that could be omitted.
Stranded prepositions can also arise in passive voice constructions and other uses of passive past participial phrases, where the complement in a prepositional phrase can become zero in the same way that a verb's direct object would: it was looked at; I will be operated on; get your teeth seen to.
The same can happen in certain uses of infinitive phrases: he is nice to talk to; this is the page to make copies of.
Clause
A clause is a grammatical unit built around a verb that typically contains a subject and a predicate. Understanding clauses is essential because they are the core building blocks of every sentence you read, write, or speak.
What makes a clause?
At minimum, a clause needs a verb (the predicate) and, in most cases, a subject — the person or thing the verb says something about. The predicate can also include objects, complements, and modifiers.
- She laughed. — subject (she) + verb (laughed)
- The manager approved the budget yesterday. — subject + verb + object + modifier
Sometimes the subject is left out. This happens regularly in imperative sentences and non-finite clauses:
- Sit down. — no visible subject, but "you" is understood
- Walking home, I noticed the shop was closed. — the -ing clause has no stated subject
Types of clauses
There are two main types:
-
Independent clause (also called a main clause) — can stand on its own as a complete sentence. It contains a finite verb.
- I missed the bus.
-
Dependent clause (also called a subordinate clause) — cannot stand alone and needs an independent clause to make sense.
- Because I overslept — incomplete on its own
Combine them and you get a complex sentence:
- I missed the bus because I overslept.
A simple sentence has one independent clause. More complex sentences combine independent and dependent clauses in various ways.
Quick check: If you can remove a group of words from a sentence and it still has a subject + finite verb and makes sense on its own, that group is likely an independent clause.
Why clauses matter
Recognizing clause boundaries helps you punctuate correctly, avoid run-on sentences, and build more varied, natural-sounding writing. Once you can spot where one clause ends and another begins, sentence structure becomes much easier to manage.
Ready to practice? Try Complex Sentence for the basics, then move on to Complex Sentence: Adverbials or Participle Clauses: Shortening Sentences with -ing and Having + Past Participle to deepen your skills.
Word Order
The primary word orders that are of interest are
- the constituent order of a clause, namely the relative order of subject, object, and verb;
- the order of modifiers (adjectives, numerals, demonstratives, possessives, and adjuncts) in a noun phrase;
- the order of adverbials.
Constituent word order is defined in terms of a finite verb (V) in combination with two arguments, namely the subject (S), and object (O).
There is a difference between grammatical word order and natural word order. In many languages, topicalization and questions can change the grammatical word order.
Examples
A: [Kate loves who/Who does Kate love?] (SVO/OSV)
B: [She loves Mark/Mark is who she loves.] (SVO/OSV)
In the (A) sentences, the first one is used when putting emphasis on who Kate loves, and the second is used with more of a quizzical tone. English uses stress and tone to emphasize different aspects of the sentences, which can also change the word order, as shown above.
In the (B) sentences, the first one is more likely to be used by a native English speaker. The second sentence is grammatical as well, but less likely to be said in natural speech. This is because English uses the SVO structure in regular sentences, but is able to answer questions using the same structure that was used in the sentence.
In English, you can change the word order depending on what you want to emphasize.
B2 | Upper Intermediate
B2, or Upper Intermediate, is the fourth level on the CEFR scale. It marks the point where you move from "getting by" to genuinely comfortable communication — handling complex topics, expressing nuanced opinions, and understanding most of what you read or hear in real-world contexts.
What a B2 user can do
At this level, you're expected to:
- Understand complex texts on both concrete and abstract topics, including technical discussions in your own field.
- Follow extended speech and lectures, even when the structure isn't entirely clear, as long as the topic is reasonably familiar.
- Interact fluently and spontaneously enough that conversations with native speakers flow naturally — without strain on either side.
- Produce clear, detailed text on a wide range of subjects, using connectors and cohesive devices to build well-structured arguments.
- Explain and defend a viewpoint on a topical issue, weighing the advantages and disadvantages of different options.
- Recognize implicit meaning — reading between the lines in demanding, longer texts.
What B2 grammar looks like in practice
B2 is where grammar stops being about isolated rules and starts being about flexibility and precision. You're expected to control structures like:
- Advanced conditionals and mixed conditionals — moving beyond simple if-clauses to express hypothetical and counterfactual meaning.
- Passive voice in varied tenses and contexts, not just present and past simple.
- Reported speech with correct sequence of tenses, including backshifting and reporting verbs.
- Participle clauses and the distinction between participles and gerunds.
- Comparative and superlative structures beyond basic -er/-est, including double comparatives and qualifying expressions.
Errors still happen at B2, but they rarely cause misunderstanding. The goal is controlled, flexible use of language across social, academic, and professional settings.
How B2 fits in the CEFR progression
B2 builds directly on the foundations of B1 (Intermediate) and prepares you for C1 (Advanced). Many university entrance exams, professional certifications, and immigration requirements target B2 as the minimum standard.
Self-check: If you can read a newspaper editorial, follow most of a TED talk without subtitles, and write a clear essay arguing a position — you're likely operating at B2.
Ready to test yourself? Try Is your English level B2/Upper Intermediate? or practise specific B2 grammar with challenges like Basics. Advanced Conditionals And "wish", Basics. Passive Voice, and Sequence of Tenses in Indirect Speech.
Difficulty: Hard
Hard difficulty. Difficulty levels represent author's opinion about how hard a question or challenge is.