Can, should and must

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A modal is followed by the base verb: can help, should check, must leave. It does not add s for a singular subject. Can can express ability or permission; should often gives advice; must can express a strong obligation. The situation determines the intended meaning.

Try the three exercise formats

Examples to compare

  • She can help.
  • You should check the address.
  • You do not have to print it; a screen copy is fine.

Watch the meaning and the limits

Must not prohibits an action. Do not have to says an action is unnecessary; it does not prohibit it. Advice and rules are different speech acts. The examples are fictional language situations, not instructions about real legal or medical obligations.

Read each example aloud, then change one detail to make a sentence you could use. Continue with focused practice when you want a different set.

Common mistakes and how to fix them

Mistake: She can helps us.

Use: She can help us.

After can, use the base verb help without an s.

Try the pattern

3 choose questions · 2 sentence completions · 2 word gaps. Read the reason after every answer. No timer.

Typed answers stay on this page. This guided set checks the requested construction; it does not judge general writing. Read the accepted answers and reasons.

Use it in your own sentence

Write one sentence about your own routine or situation. Check the subject, verb form and intended meaning against the rule above. A different sentence may need a different form: these exercises accept the reviewed answers for their stated context.

Try the next practice set, or choose another grammar point.

All drill answers and reasons

  1. She can ___ us tomorrow.

    Choices: help / helps / helping

    Accepted: help

    A modal takes the base form help.

  2. Printing is optional. You ___ print it.

    Choices: do not have to / must not / cannot

    Accepted: do not have to

    Do not have to means it is unnecessary, not forbidden.

  3. Choose the prohibition: You ___ enter this fictional staff-only room.

    Choices: must not / do not have to / might

    Accepted: must not

    Must not expresses a prohibition.

  4. Printing is optional. Complete using have to in the negative: You ___ print it.

    Accepted: do not have to / don’t have to

    Do not have to means unnecessary, rather than prohibited.

  5. Complete using should and check: You ___ the address.

    Accepted: should check

    Should is followed by base-form check to give advice.

  6. She can ___ us. Use help in the correct form.

    Accepted: help

    A modal is followed by the base verb without s.

  7. You must ___ enter this fictional staff-only area. Add the full negative word.

    Accepted: not

    Must not expresses a prohibition.

Practice questions

How do the three exercise formats work?

Choose asks you to pick an answer. Complete the sentence asks you to type the missing phrase. Fill in the word asks for one word, or no article where stated. Every checked answer includes a reason.

Which typed answers are accepted?

Use the form and meaning requested in the prompt. Reviewed alternatives and contractions are accepted where they fit. Capital letters, surrounding spaces, straight or curly apostrophes and a final full stop, question mark or exclamation mark do not affect marking. The answer reference lists the accepted forms.

Are my typed answers sent or saved?

Typed answers stay on this page in your browser. They are not sent to the server or saved. If device progress is available, completing a set records only the activity and study points on this device.

Can this check my own writing or certify my level?

No. This is a small guided set with reviewed answers, not a general grammar checker or a level certificate. An unlisted answer does not mean it is always wrong in English. Read the prompt and the explanation for this construction.

Further reference: Cambridge English Grammar Today. The explanations, examples and exercises here are original; each lesson covers a useful pattern rather than every exception.