单项选择题


A．has been being used
B．are used
C．has been used
D．were used
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单项选择题
A．in whichB．with whichC．for whichD．of which
A．in which
B．with which
C．for which
D．of which
单项选择题
A．so thatB．suchC．soD．such that
A．so that
B．such
C．so
D．such that
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