单项选择题

Scientists say it may be ten years ______ this medicine was put to use.

A．since
B．before
C．after
D．when
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Here is my card. Let's keep in ______ .
A．touch
B．relation
C．connection
D．friendship
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It seems that there is ______ that I can't do.
A．nothing
B．anything
C．everything
D．none
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