We spent the morning wrangling thirty tourists, half of whom wandered off to take selfies with a very angry moose.
When a relative pronoun follows a preposition (like "of"), we must use the object form "whom" for people, not "who." Using "half of them" would result in a comma splice because "them" is a personal pronoun, not a relative pronoun.
By noon, we had lost five expensive cameras in the lake, all of which belonged to me, thankfully!
"All of which" is correct because "cameras" are things (requiring "which"). "Neither of which" is incorrect because "neither" only refers to exactly two items, but here there are five cameras. "All of them" would cause a comma splice.
Relative clause
A relative clause is a dependent clause that modifies a noun, typically introduced by a relative pronoun (who, whom, whose, which, that) or relative adverb (where, when, why). The man who lives in this house has not been seen for days. They split into restrictive (essential to the meaning, no commas) and non-restrictive (extra information, set off by commas).
The split matters because the comma changes the meaning: My brother who lives in Paris (one of several brothers) vs. My brother, who lives in Paris, (my only brother). Getting comma placement right is one of the highest-leverage moves at B2+.
Pronoun
A pronoun is a small, closed class of words that stands in for a noun or noun phrase. The main types: personal (I, you, he, she, it, we, they) plus their object (me, him) and possessive (my, mine) forms; demonstrative (this, that); relative (who, which, that); interrogative (who, what); and reflexive (myself, yourself).
Pronouns are how English avoids endlessly repeating names. The catch: their meaning depends entirely on context, so unclear pronoun reference (Tom told Mike that he was wrong — who's he?) is one of the most common writing problems.
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.
Punctuation
Punctuation is the set of visual marks — periods, commas, question marks, colons, semicolons, apostrophes, quotation marks, hyphens and dashes — that show readers where sentences begin and end, where pauses go, and how parts of a sentence relate.
Punctuation does two jobs: it follows the rhythm of speech (where you'd pause aloud) and it marks the structure of clauses. Mismatch the two and writing reads either as breathless or as choppy. Mastering the basics is a small investment with huge returns — clear punctuation makes prose look careful and considered.
C1 | Advanced
C1 is the advanced level in the CEFR framework, sitting between B2 and C2. At C1 you stop translating in your head and start thinking in English — handling specialised articles outside your field, picking up implicit meaning, and writing structured arguments on complex topics.
Grammatically, C1 means natural use of inversion (Rarely have I seen…), mixed and advanced conditionals, subjunctive forms in formal contexts, and cleft sentences for emphasis. Most university programmes for non-native speakers and many professional certifications set C1 as their entry standard.
Difficulty: Hard
The Hard difficulty tag marks questions and challenges aimed at upper-intermediate to advanced learners — typically B2 and above. Expect interacting rules, edge cases, distractors that look right at first glance, and contexts where the surface meaning and the grammatical answer don't match.
Filter by Hard when you're past the basics and want material that genuinely tests your understanding. These questions catch the gaps your textbook didn't — register-sensitive choices, exception cases, mixed conditionals, the difference between would have been and had been.