Complete the time-traveler's rather confusing diary entry.
I am stuck in 1899. I ______ my time machine's keys yesterday, and now I'm living in a barn with a very confused horse.
The correct answer is lost.
In English, when a sentence includes a finished time word like "yesterday," "last week," or "in 1999," you must use the Past Simple (lost).
Note for Romance language speakers: Even though your native language might use a perfect tense here (like he perdido, j'ai perdu, or ho perso), English strictly separates finished past time from the Present Perfect!
Verb
A verb is a word that expresses an action, a state, or an occurrence — the engine of every English sentence. Most verbs have five forms: base (go), -s form (goes), past tense (went), past participle (gone), and -ing form (going). The verb be is the major exception with eight forms; modal verbs like can and must have fewer.
Verbs carry tense (when), aspect (how it unfolds), mood (the speaker's attitude), and voice (active vs passive). Mastering them is foundational — virtually every other grammar topic depends on getting verbs right.
Verb tense
Verb tense is the verb form that signals when the action happens. English has three time references — past, present, and future — combined with three aspects (simple, progressive, perfect, plus perfect progressive) to give twelve standard tense forms in total.
Each tense form carries specific meaning beyond just "when". I worked (simple past) and I have worked (present perfect) both refer to past action, but only the second connects that action to the present. Picking the right tense is what makes English narratives clear; the wrong one makes meaning subtly drift.
Past tense
The past tense is how English talks about events finished before now. It comes in four flavours: simple past (I walked) for completed events, past progressive (I was walking) for actions ongoing at a past time, past perfect (I had walked) for events before another past event, and past perfect progressive (I had been walking) for ongoing events leading up to a past point.
Choosing the right one is what makes past narratives clear instead of murky. When I arrived, she ate dinner is technically grammatical but means something different than had eaten (already done) or was eating (in progress when you arrived).
Simple tense
The simple aspect is the unmarked verb form — no progressive -ing, no have + past participle. I go, I went, I will go are simple; I am going, I have gone, I had gone are not. The simple aspect typically marks a single completed action (Brutus killed Caesar), a repeated/habitual action (I go to school every day), or a permanent state (We live in Dallas).
The simple aspect is the foundation everything else builds on. Once it's automatic, switching into progressive (ongoing) or perfect (completed-relative-to-now) becomes a small adjustment rather than a fresh decision.
Irregular verb
An irregular verb doesn't form its past tense and past participle by adding -ed — it changes shape in unpredictable ways: go → went → gone, eat → ate → eaten, put → put → put, take → took → taken. English has roughly 200 irregular verbs in common use, and many of them are the most frequently used verbs in the language (be, have, do, say, get, make, go, come).
Because the most-used verbs are irregular, you can't avoid them — they show up in every sentence. Memorising the three principal parts (base, past tense, past participle) of the top 100 is one of the highest-leverage moves at A2/B1.
B1 | Intermediate
B1 is the intermediate level in the CEFR framework — the point where you stop relying on memorised phrases and start handling everyday English independently. At B1 you can describe experiences, explain opinions, and follow most clear standard speech on familiar topics like work, travel, and hobbies.
Grammatically, B1 means combining tenses with precision, building complex sentences, and starting to use passive voice, modal verbs for necessity and possibility, and verb patterns (gerund vs. infinitive). Knowing your level shapes what you study next: pushing too far ahead frustrates you; staying below your level wastes time.
Difficulty: Medium
The Medium difficulty tag marks questions and challenges in the middle of the difficulty range — typically suitable for A2 to B1 learners. Expect a single rule with realistic distractors, longer sentences, and contexts where you have to think before answering rather than reading off the obvious choice.
Filter by Medium when you're past the absolute basics and ready to consolidate. It's the level where most lasting progress happens — easy enough that you can finish without exhausting concentration, hard enough that getting it right means you've actually understood.