The present continuous tense is formed using the auxiliary verb "am," "is," or "are" followed by the present participle (-ing form) of the main verb. In this case, the subject is "the children," which requires "are" as the auxiliary verb, and the present participle of "to swim" is "swimming." So, the correct answer is "are swimming."
Present tense
The present tense in English has four forms: simple present (I work) for habits, general truths, and stative descriptions; present progressive (I am working) for actions happening right now or temporary situations; present perfect (I have worked) for past actions with present relevance; and present perfect progressive (I have been working) for ongoing actions continuing into the present.
The simple/progressive distinction is one of the trickiest jumps for learners — I work in Paris (habitual) and I'm working in Paris (temporary, right now) feel almost identical but signal different things. Pick wrong and your meaning subtly shifts.
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.
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.
Progressive tense
The progressive aspect (also called continuous) marks an action as ongoing at the time of reference, formed with be + present participle (-ing): I am working, She was reading, They will be travelling. It signals temporary or in-progress events — the contrast with the simple aspect (I work = habit; I'm working = right now) is one of the most-used distinctions in English.
Some verbs (stative verbs like know, believe, own, belong) don't normally take the progressive — I'm knowing the answer sounds wrong. Recognising stative vs dynamic verbs is what stops you from over-applying the rule.
A1 | Elementary | Beginners
A1 is the starting level of the CEFR framework — the entry point into English. At A1 you can introduce yourself, ask and answer simple personal questions, recognise common signs and instructions, and have short slow-paced conversations on very familiar topics.
Grammatically, A1 covers the building blocks: present-tense forms of be, have, and do; basic word order; simple questions; and the most common determiners, pronouns, and prepositions. Knowing your level matters — A1 material teaches the foundations every later level builds on, while a B1 textbook will overwhelm you. Start here and progress is fast.
Difficulty: Easy
The Easy difficulty tag marks questions and challenges aimed at beginners — typically A1 or early A2 level. Expect single-rule focus, short sentences, common everyday vocabulary, and one clear correct answer. Distractors usually rule themselves out quickly.
Filter by Easy when you're rebuilding fundamentals, warming up before harder material, or testing whether you've truly internalised a basic rule before moving on. Easy doesn't mean trivial — it means the rule itself is unambiguous and the context doesn't pile on extra complications.