ZD(J)9系列电动转辙机的滚轮通过()的作用,使锁闭柱(检查柱)抬起或落入锁闭(表示杆)槽内,达到检测()的作用。
参考答案:左右支架;道岔状态
The reason _____ he could not go there was _____ his grades were too low.
A.why ; because
B.that; because
C.why; that
D.that; that
钻进过程中水龙头的中心管带动钻柱旋转。