1. you must sign the form twice ->...................
2. visitors to the zoo mustn't feed the animals ->.........
3. all passengers must wear seat-belts ->.................
4. somebody should pick the visitors up from the airport ->......................
5. it ín't neccessary for jim to take the exam again (need )->.......
chuyễn sang passive voice
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Sinh Học lớp 12
