3. Read the Learn this! box and complete the rules. Use must, mustn't, needn't and don't have to. Use your answers to exercise 2 to help you.
(Đọc hộp Learn this! và hoàn thành các quy tắc. Dùng must, mustn't, needn't and don't have to. Sử dụng các câu trả lời trong bài 2 để giúp bạn.)
LEARN THIS! must, mustn't and needn't/ don't have to
a. We use (1) _____ to say that something is necessary or very important to do.
b. We use (2) _____ and (3) _____ to say that something is not necessary.
c. We use (4) _____ to say that something is prohibited (a negative order)
Note: We can also use passive forms after modal verbs.
Helmet must be worn at all times.
1.must
2. needn’t
3. don’t have to
4. mustn’t