RC串联电路在工程上应用很广，电容器放电的变化规律是（）。
A.瞬间放完电
B.永远也放不完电
C.放电初期仍保持原电压
D.放电电流先小后大
参考答案：C
硅酸盐水泥凝结的时间是( )。
A．初凝不得迟于45 min，终凝不得迟于390 min
B．初凝不得早于45 min，终凝不得迟于390 min
C．初凝不得迟于45 min，终凝不得早于390 min
D．初凝不得早于45 min，终凝不得早于390 min
---Can you let me know yesterday?
---Because the traffic was bad.
A．why did you come late
B．why you came late
C．why do you come late
D．why you come late
