专四单项The students in the dormitories were forbidden,unless th

专四单项
The students in the dormitories were forbidden,unless they had special passed,__ after 11pm.
stay out,为什么要用不定式?
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In order to be a good scientist,____.
A.mathematics is urgent
B.one should have the mathematiecs
C.one must understand mathematiecs
D.mathematics is important to be understood
为什么选C?
=
"Did the audience participate in the play?"
"Yes,those actors __ to involve the audience."
A.whom it was the function
B.of whom the function was
C.whose function it was
D.whose were the function
为什么选C?顺便说一下不选其它选项的原因.
THX:)