进入轿厢顶时，首先切断轿厢顶上检修盒上的_，使电梯无法运行，再将有关开关置于检修状态。
参考答案：急停开关
Doing enough exercise _____ our health. [ ]
A. is good for
B. is good to
C. are good for
D. are good at
填料塔的作用原理如何？
