Question

To make our city more beautiful, rubbish ________ into the river.

1. A.
   needn't be thrown
2. B.
   mustn't be thrown
3. C.
   can't throw
4. D.
   may not throw

Answer 1

B
解析：
剖析：這是含有情態動詞的被動語態。首先應排除C和D，因為它們是主動語態；
含有情態動詞的被動語態的構成應該是：“情態動詞+be+及物動詞的過去分詞”，needn't是“不必”=don't have to；
mustn't是“禁止，不準”之意，故選B。