以下属于井口不能发信号的故障原因的是（）。
A、减速器故障
B、摇台位置开关的故障
C、推车机位置开关的故障
D、信号发送机的原因
参考答案：D
We enjoy _____ the explorer talk about his wonderful _____ of rocks. [ ]
A. listen to; collect
B. listening to; collection
C. listen to; collection
D. listening to; collecting
