单项选择题

Everyone is busy working. You can't stay here ______ you keep quiet.

A．when
B．once
C．if
D．unless
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______ did he give you much advice
A．In what
B．On what
C．What
D．On which
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He found it necessary for us ______ from each other.
A．to help and learn
B．helping and learning
C．to learn and help
D．learning and helping
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