单项选择题

It is not until recently ______ there are many different kinds of hearing defects.

A．have the scientists discovered
B．the scientists have discovered
C．that the scientists have discovered
D．that will the scientist have discovered
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单项选择题
He actually didn't see the man ______ the room, but he heard them ______ in it.
A．to enter, laugh
B．enter, to laugh
C．to enter, laughing
D．enter, laughing
单项选择题
I regret ______ you the news that he is going to leave us for good.
A．to tell
B．telling
C．having told
D．to have told
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