联合站内所有运转设备、储罐、压力容器要做到（）检查，维护保养，保证安全生产。
A.定期
B.随时
C.24h
D.不定期
参考答案：A
The bus _______ at 8:30 p.m., so I have to be at the station by 8:10 at the latest.
A．has left
B．would leave
C．leaves
D．will have left
y=x3+ax+1的一条切线方程为y=2x+1，则a=（ ）。
