Complete the passage with must or mustn’t.
When you travel on the London Underground, you (1) _______________ smoke. You (2) _______________ always buy a ticket and if you have a travel card, you (3) _______________ use it on the same day. When a train arrives at the station, you (4) _______________ stand back. You (5) _______________ be polite to the staff.
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Sinh Học lớp 12
