下列行为有利于水污染控制的是（）
A、利用畜禽粪便厌氧发酵生产沼气
B、给农作物大量施肥或喷洒农药
C、工业废水不经处理就排放
参考答案：A
立体仓库中作业高度在12米以上，需要使用堆垛机械，应该选择（）。
A.叉车
B.无轨巷道堆垛起重机
C.有轨巷道堆垛起重机
D.堆垛起重机
Never______ such a difficult problem. It took me almost half an hour to work it out.
A．had I come across
B．I had come across
C．did I come across
D．I did come across
