学校建楼运来x吨水泥，每天用去3.4吨，用了y天，还剩______吨．
x-3.4y（吨），
答：还剩x-3.4y吨；
故答案为：x-3.4y．
—Li Lin took the 8:00 bus to Fuzhou this morning.
—Really? He _________ a fast train. It’s much more comfortable to travel by fast train.
A．could have taken
B．should take
C．must have taken
D．can take
反时限强励限制，电流越大，该限制的动作时间就越（）。
A.快
B.慢
C.不变
