Help the frantic traveler text his friend about his arrival.
I'm finally ___ train to London! I'll see you in an hour.
The correct answer is on the.
While it feels logical to be "in" a vehicle, English uses on for large public transport where you can stand up and walk around (like a bus, train, or plane). We use "the" because it is a specific train.
Preposition
If you've ever written I'm interested on you (should be in) or I'm good on football (should be at) — you've hit prepositions' main pitfall. Their choice is mostly idiomatic, not logical, and rarely matches what your native language does. Memorising the right preposition for each common verb and adjective is what stops your speech from sounding subtly off.
A preposition is a small word linking a noun or noun phrase to other parts of the sentence: in, on, at, to, from, with. Marks time, place, manner, or abstract relationships. Choice is largely idiomatic, especially in fixed combinations (depend on, good at, afraid of).
Article
If you speak a language without articles — Russian, Japanese, Polish, Korean, Mandarin — articles in English are probably the single most stubborn topic you face. The rules feel small but the wrong choice (I went to the home instead of I went home) immediately marks you as non-native. Mastering articles is the highest-leverage move you can make for sounding natural.
Articles are a small group of determinatives — a, an, the, plus the zero article (no article at all) — that signal whether a noun is specific or general. The choice depends on the listener's knowledge, the noun type, and idiomatic context.
B1 | Intermediate
If you can hold a conversation about your weekend, explain why you're late, and follow a short news story without panicking — but still feel lost in fast or technical English — you're probably operating at B1. Knowing this matters: study material at the wrong level either bores you or burns you out, and B1 is the typical target for travel, casual work, and most everyday social English.
B1 is the intermediate level in the CEFR framework, where you handle everyday English independently and start combining ideas with complex sentences, passive voice, and modal verbs.
Difficulty: Medium
If easy questions feel too obvious but hard questions leave you guessing, you're probably ready for Medium — the level where most real learning happens. It pushes just enough to expose the rules you don't quite have yet, without burying you in edge cases. This is where steady fluency is built, one well-aimed challenge at a time.
The Medium difficulty tag marks middle-range challenges — typically A2 to B1. One rule per question, realistic distractors, and contexts that require active thought rather than instant recognition.