能够远距离操作的低压电器是（）。
A、断路器
B、接触器
C、刀开关
D、熔断器
参考答案：B
Climbing is one of ________, I think.[ ]
A. the most difficult activity
B. the most difficult activities
C. most difficult activity
D. most difficult activities
什么叫做岩体，它与岩石有何区别？
