I am currently at a loss to explain how the suspect managed to delete the classified files. He claimed he did it by no article mistake, but I was under the impression that the system required a complex password and two-factor authentication.
at a loss: This is a fixed idiom meaning "uncertain" or "unable to know what to do or say," and it always requires the indefinite article "a".
by mistake: In English, many phrases starting with "by" that describe how something happens (e.g., by chance, by accident, by mistake) do not take an article.
under the impression: This fixed expression means "believing something (often wrongly)" and always uses the definite article "the".
Article
Articles are a small group of determinatives that signal whether a noun refers to something specific (the book) or something general (a book). English has three: the definite article the, the indefinite articles a/an, and the zero article — the meaningful absence of any article (Coffee keeps me awake).
Articles are one of the trickiest parts of English for non-native speakers because the choice depends on context, not just the noun itself. Get them right and your writing instantly sounds more natural; miss them and even simple sentences feel "off" to a native ear.
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.
Phrase
In grammar, a phrase is a group of words (sometimes a single word) that functions as a single unit in a sentence — but doesn't include a subject + verb pair the way a clause does. Common types: noun phrase (the old red car), verb phrase (has been running), prepositional phrase (on the table), adjective phrase (incredibly tired), adverb phrase (very quickly).
Phrases are the building blocks between individual words and full clauses. Recognising them helps you see how sentences hold together — and where you can break, expand, or rearrange them without losing meaning.
Idiom
An idiom is a fixed expression whose meaning isn't predictable from the words it contains. Kick the bucket doesn't mean physically kicking a bucket — it means to die. Spill the beans means to reveal a secret. It's raining cats and dogs means it's pouring rain. The cultural meaning has fully replaced the literal one.
English is dense with idioms, and recognising them is the difference between feeling lost in a casual conversation and following along easily. They can't usually be translated word-for-word into other languages — they have to be learned as whole units, like vocabulary.
Collocations
Collocations are combinations of words that habitually occur together in a fixed order — make a decision (not do a decision), strong coffee (not powerful coffee), heavy rain (not thick rain). The grammar would allow either pairing, but native speakers consistently pick one and reject the other. Common patterns include verb + noun, adjective + noun, adverb + adjective, and adverb + verb.
Learning vocabulary as collocations rather than isolated words is the single fastest way to sound natural in English. It's the difference between I made a big mistake and I did a big mistake — small, but immediately noticeable.
B2 | Upper Intermediate
B2 is the upper-intermediate level in the CEFR framework, sitting between B1 and C1. At B2 you can read editorials, follow most TED talks without subtitles, and hold extended conversations on abstract topics — including topics outside your everyday life.
Grammatically, B2 means flexible control of mixed conditionals, passive voice across tenses, reported speech with proper backshifting, and participle clauses. B2 is the standard target for university entrance exams (IELTS 5.5–6.5, TOEFL 87–109) and most skilled-migration thresholds — knowing whether you're there shapes your study plan.
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.