The correct answers are must, don't have to, and must not.
Must is used here for a strong personal recommendation — the blogger feels very strongly about it. Don't have to means speaking Japanese is not necessary — you can manage without it. Must not expresses prohibition — eating on the train is not allowed because it is considered rude. Notice the important difference: don't have to = it's not necessary (you have a choice), while must not = it's prohibited (don't do it!).
Modal verb
A modal verb is a special class of auxiliary — can, could, may, might, must, shall, should, will, would — that adds shades of meaning around possibility, ability, permission, obligation, or speculation. I can swim (ability), You should rest (advice), It might rain (possibility), You must leave (obligation).
Modals are grammatically peculiar: no -s in the third person (she can, not she cans), no infinitive, no participle, followed by the bare verb (I can swim, never I can to swim). Mastering them is the move from describing facts to expressing how you feel about them — likelihood, necessity, recommendation.
Negation
Negation in English usually places not after the auxiliary or modal verb: I am not going, She does not know, You must not go. When there's no auxiliary, you add do-support: I go → I do not go. Most combinations contract: don't, can't, won't, isn't.
The trickiest rule for many learners: double negatives are not standard English. I didn't see nothing is non-standard; the standard forms are I saw nothing or I didn't see anything. Negative words like never, nobody, nothing already carry the negation — adding not on top doubles up.
Auxiliary verb
An auxiliary verb (or "helping verb") is a verb that combines with a main verb to add grammatical meaning — questions, negation, tense, aspect, voice, or modality. The English auxiliaries are forms of be, have, do, plus the modal verbs (can, could, will, would, should, may, might, must).
Auxiliaries are what let you build past tense (have gone), continuous aspect (is going), passive voice (was eaten), and questions (Do you know?). Without them, you can't form most of the structures you need beyond the simple present and past — they're the engine that powers half the tense system.
A2 | Elementary | Pre-intermediate
A2 is the elementary level in the CEFR framework, sitting between A1 and B1. At A2 you can handle routine exchanges — ordering food, asking directions, making small talk — and describe your immediate environment in simple sentences.
Grammatically, A2 introduces past simple and past continuous, present perfect for experiences, basic modal verbs, and the first conditional. You're also picking up collocations and learning which verbs take gerunds vs. infinitives. Knowing your level here is the difference between confident progress and frustration: A2 material consolidates the basics; B1 will overwhelm you.
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.