Since the getaway car had a flat tire, the thieves decided to take the city bus.
"Since" is a subordinating conjunction that introduces a full adverb clause of reason (subject + verb). "Because of" and "due to" are prepositions that must be followed by a noun phrase.
The police caught them easily because they paid the bus driver with the stolen ancient coins.
"Because" introduces the full clause explaining the reason. "Because of" and "due to" are incorrect because they are followed by a full clause here, not a noun phrase.
The judge denied them bail, as they were still wearing their ski masks in the courtroom.
"As" functions just like "because" or "since" to introduce an adverb clause of reason.
Clause
A clause is a grammatical unit built around a verb — typically a subject plus a predicate (She laughed; The manager approved the budget). Clauses come in two types: independent clauses stand alone as complete sentences; dependent clauses need an independent clause to make sense (Because I overslept — incomplete on its own).
Spotting clause boundaries is the foundation of correct punctuation. Once you can see where one clause ends and another begins, comma rules, run-on sentences, and complex sentence structure stop being mysteries.
Dependent clause
A dependent clause (also called a subordinate clause) is a clause that has a subject and a verb but can't stand alone as a complete sentence. It needs an independent clause to attach to. Because I overslept is a dependent clause; I missed the bus because I overslept is a complete sentence.
Dependent clauses come in three main types: noun clauses (acting as a noun: I know that he likes me), adjective/relative clauses (modifying a noun: the dwarf who has no beard), and adverbial clauses (modifying a verb or whole clause: Wherever she goes). They're how English packs more information into a single sentence.
Conjunction
A conjunction is a word that connects other words, phrases, or clauses. English has two main types: coordinating conjunctions join units of equal weight (and, but, or, so, yet, for, nor — the FANBOYS), while subordinating conjunctions introduce dependent clauses (because, although, if, when, while, since, unless).
Conjunctions are how you build compound and complex sentences instead of stacking short ones. The choice of conjunction signals the relationship between the ideas — addition, contrast, cause, condition, time — so picking the right one shapes the whole meaning.
Preposition
A preposition is a small word that links a noun or noun phrase to other parts of the sentence — usually marking time, place, or relationship: in, on, at, to, from, with, over, under, between, during. The book on the table, We met at noon, She lives in Berlin.
Prepositions are deceptively small. Their meaning shifts dramatically by collocation (depend on, good at, afraid of), and their choice rarely translates directly between languages. Picking the right preposition is one of the trickiest, most idiomatic-sounding parts of English.
Complex sentence
A complex sentence combines an independent clause with at least one dependent (subordinate) clause: I missed the bus because I overslept. The dependent clause adds extra information — usually about time, reason, condition, or which thing is meant — but can't stand alone. It's introduced by a subordinating conjunction (because, although, if, when, while) or a relative pronoun (who, which, that).
Mastering complex sentences is the move from simple, choppy writing to prose that links ideas. It's also where comma decisions get interesting — placement depends on which clause comes first.
Humor
The Humor tag marks questions and challenges where the author has tried — subjectively, deliberately — to make the practice itself entertaining. Expect characters, scenarios, and storylines that play with absurdity: zombies, alien tourists, a chef's disaster, a roommate's complaint. The grammar rule is real; the wrapping isn't.
Humor matters because grammar drills are forgettable. Tying a rule to a story your brain wants to keep makes it stick. Filter by Humor when motivation is what you're short on, not study time.
B1 | Intermediate
B1 is the intermediate level in the CEFR framework — the point where you stop relying on memorised phrases and start handling everyday English independently. At B1 you can describe experiences, explain opinions, and follow most clear standard speech on familiar topics like work, travel, and hobbies.
Grammatically, B1 means combining tenses with precision, building complex sentences, and starting to use passive voice, modal verbs for necessity and possibility, and verb patterns (gerund vs. infinitive). Knowing your level shapes what you study next: pushing too far ahead frustrates you; staying below your level wastes time.
Difficulty: Medium
The Medium difficulty tag marks questions and challenges in the middle of the difficulty range — typically suitable for A2 to B1 learners. Expect a single rule with realistic distractors, longer sentences, and contexts where you have to think before answering rather than reading off the obvious choice.
Filter by Medium when you're past the absolute basics and ready to consolidate. It's the level where most lasting progress happens — easy enough that you can finish without exhausting concentration, hard enough that getting it right means you've actually understood.