推车机推车时，翻矸机能翻；翻矸机翻车时，推车机不能推。
参考答案：错
When whistle signals are used for launching lifeboats，one short blast means（）.
A.use the float-free method only
B.lower all boats
C.raise all boats
D.drill is over，secure all boats
沼气有哪些好处？
