Help the new employee understand the office dynamics by choosing the correct word.
The breakroom coffee machine, _____ sounds like a dying pterodactyl, makes surprisingly excellent espresso.
The correct answer is which.
Because the clause is separated by commas (making it a non-defining relative clause that adds extra information), we must use which for things. We cannot use that after a comma in a relative clause!
Relative clause
- ✅ The man who called is my uncle. — restrictive (essential: which man?)
- ✅ My uncle, who lives in Paris, called. — non-restrictive (extra info, commas)
- ❌ My uncle that lives in Paris — wrong (that can't introduce non-restrictive)
- ✅ The book that I read = The book I read — restrictive (pronoun optional)
Relative clauses modify nouns using who/whom/whose/which/that or where/when/why. Restrictive = essential, no commas, that OK. Non-restrictive = extra, needs commas, uses which/who (never that).
Rule: if you can remove the clause and still know which noun is meant → non-restrictive (commas). If removing it makes the noun ambiguous → restrictive (no commas).
Pronoun
- ✅ between you and me — ❌ between you and I (objective case after preposition)
- ✅ its colour — ❌ it's colour (it's = it is)
- ✅ She did it herself. — reflexive pronoun
- ✅ The person who called… — relative pronoun
Pronouns replace nouns: personal (I/me/my), demonstrative (this/that), relative (who/which/that), interrogative (who?/what?), reflexive (myself), indefinite (everyone/nobody). They carry case that nouns have lost.
Trap: pronouns are where English case still matters: I vs me, who vs whom, its vs it's. Get these wrong and it's instantly noticeable.
Comma
- ✅ apples, pears, and figs — list separator
- ✅ My brother, a doctor, called. — non-essential info set off by commas
- ✅ I went home, and she stayed. — comma before conjunction joining two clauses
- ❌ I went home and she stayed. — missing comma (two independent clauses need one before and)
The comma ( , ) separates elements within a sentence: list items, non-essential phrases, introductory words, and clauses joined by coordinating conjunctions.
Rule: if two independent clauses are joined by and/but/or, put a comma before the conjunction. If it's just a compound verb (same subject), no comma.
Clause
- I missed the bus. — ✅ independent clause (stands alone)
- Because I overslept. — ❌ fragment (dependent clause, can't stand alone)
- Because I overslept, I missed the bus. — ✅ dependent + independent = complete sentence
- I missed the bus, and I was late. — ✅ two independent clauses joined by and
A clause is a unit built around a verb with a subject. Independent = can stand alone. Dependent = needs an independent clause to complete it.
Test: does the group of words have a subject + verb AND can it be a sentence on its own? Yes → independent clause. Has a subject + verb but feels incomplete → dependent clause.
B2 | Upper Intermediate
- ✅ If I had studied harder, I would have passed. — third conditional
- ✅ The report is being reviewed by the committee. — passive progressive
- ✅ Having finished the exam, she left. — participle clause
- ✅ He denied having taken the money. — complex verb pattern
These are B2 patterns — the CEFR upper-intermediate level. At B2 you handle mixed conditionals, all passive forms, participle clauses, and can argue a point clearly. This is the level most universities and employers require.
Marker: if you can write a structured essay and debate an abstract topic, you're B2.
Medium
- If I were you, I would apologise. — one rule (second conditional), but distractors like was tempt you
- Answers require active thought, not instant pattern recognition
- Vocabulary and context are realistic, not artificially simplified
- Usually tests one rule, but the wrong answers are plausible
Medium marks middle-difficulty challenges: A2–B1, one rule tested, but with realistic distractors that require genuine understanding.
Use "Medium" when Easy feels too obvious but Hard feels overwhelming. This is where most productive learning happens — the sweet spot of difficulty.