送电后,按下起动按钮,主接触器吸合,但一动控制器,主接触器就释放,其原因是()
A.零位触头接触不良
B.安全栏开关未合上
C.接触器联锁自保线继路
参考答案:C
They will never succeed, _____ hard they try.
A.because
B.however
C.when
D.since