You may lie ______ the ground is dry.
A．which
B．that
C．where
D．unless
答案：C
A ______ identification card is required when you purchase foreign money from the Bank of China.
A．valid
B．perfect
C．beneficial
D．flexible
若2a2+3a-b=4，则
=( )．
A．2
B．4
C．8
D．16
=( )．