When ______ why he walked in without permission,he just stared at us and said nothing.
A. been asked
B. asked
C. asking
D. to be asked
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The man kept silent in the room unless ______ .
A. spoken to
B. spoke to
C. spoken
D. to speak
He was often listened ______ in the next room.
A. sing
B. sung
C. to sing
D. to to sing
What’s troubling them is ______ enough experienced workers.
A. that they have to
B. they have not
C. their not having
D. not their having
_____ his telephone number,she had some difficulty getting in touch with Bill.
A. Not knowing
B. Knowing not
C. Not having known
D. Having not know
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