图1.5-12所示电路中，t=0时闭合开关S，u1（0-）=u2（0-）=0V，则u1（0+）应为（）V。
A.6
B.4
C.0
D.8
参考答案：D
By the time he arrives in Tianjing, we ____ here for two days.
A．have stayed
B．have been staying
C．stay
D．will have stayed
There’s ____ water on the playground, so we won’t have the P.E. class there.
A．too many
B．many too
C．too much
D．much too
