单项选择题

Training astronauts- ______ not an easy thing.

A．are
B．is
C．were
D．be
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单项选择题
I invited Tom and Ann to dinner, but ______ of them came.
A．both
B．none
C．either
D．neither
单项选择题
In spite of what we said, he refused to ______ to the police station.
A．give away
B．give off
C．give himself away
D．give himself up
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