The original sentence requires the past perfect tense, which is formed using the auxiliary verb "had" followed by the past participle of the main verb. The verb "to write" is an irregular verb, and its past participle form is "written." So, the correct answer is "He had written a letter by the time we arrived."
Past tense
If you've ever told a story in English and felt the timeline get tangled — I came home, the dog ate, the cat slept — you've hit the limits of using simple past for everything. The past tense system has four forms specifically because real stories have layered timing: things that happened before other things, actions caught in progress, sequences of completed events.
The past tense has four English forms: simple past (I walked), past progressive (I was walking), past perfect (I had walked — earlier than another past event), past perfect progressive (I had been walking — ongoing up to a past point). Plus irregular verbs for the simple-past form.
Irregular verb
If you've ever said I goed or I taked and felt the sentence collapse — you've hit irregular verbs head-on. The 200 most-used English verbs include nearly every irregular one, so there's no clever shortcut: you memorise them, drill them, and let them become automatic. The good news is that once they're automatic, half your past-tense problems disappear.
An irregular verb doesn't follow the -ed past-tense pattern. Instead its past tense and past participle change shape: go → went → gone, eat → ate → eaten, take → took → taken, put → put → put. About 200 verbs in common use; most of them are also the most frequent verbs in English.
Verb
If grammar feels overwhelming, the fix is almost always to focus on verbs first. They carry the action, the time, the mood, and the voice — a single verb form decides whether your sentence reads as past or present, fact or hypothetical, active or passive. Get verbs solid and the rest of grammar suddenly looks much smaller.
A verb expresses action, state, or occurrence — the engine of every English sentence. Most verbs have five forms (base, -s, past tense, past participle, -ing); be has eight; modal verbs have fewer. Verbs carry tense, aspect, mood, and voice.
Participle
If you've ever written I should have went and been corrected to should have gone — you've hit the past participle's main rule. The participle isn't an exotic form; it's the workhorse that builds perfect tenses, passive voice, and dozens of common adjectives. Get the irregular ones automatic and your tenses fall into place.
A participle is a verb form acting as an adjective or adverb. The present participle is the -ing form (running, sitting); the past participle is -ed (regular: walked) or irregular (broken, gone, written). Participles build perfect tenses, progressive tenses, and the passive.
Perfect tense
If you've ever written I am living here for ten years (should be have lived or have been living) — you've hit the perfect tense's main puzzle. English insists that "started in the past, still true now" lives in the present perfect, not the simple present. Get this clear and a whole class of common errors disappears.
The perfect aspect marks completion relative to a point in time, formed with have + past participle: I have eaten (present perfect), She had finished (past perfect), They will have arrived (future perfect). Combinable with progressive aspect (I have been working).
A2 | Elementary | Pre-intermediate
If you can order coffee, ask for directions, and tell someone what you did yesterday — but struggle the moment the conversation drifts into anything abstract — you're operating at A2. Knowing this matters: A2 is the level where most learners plateau because they reach for B2 material too early and burn out. Stay here and your foundations get unbreakable.
A2 is the elementary level in the CEFR framework, covering routine communication and the first wave of real grammar: past simple and continuous, present perfect, basic modal verbs, first conditional, and common verb-pattern rules.
Difficulty: Easy
If a textbook leaves you confused, sometimes the issue isn't the topic — it's that the practice material is layered with extra complications. Filtering by Easy strips that away. You get one rule at a time, in plain everyday language, with no trick questions. It's how you make a shaky foundation solid before stacking more on top.
The Easy difficulty tag marks beginner-level questions and challenges — typically A1 or early A2. Single-rule focus, short sentences, common vocabulary, one clear correct answer.