井下空气中一氧化碳的主要来源有（）。
A.煤炭自燃
B.瓦斯、煤尘爆炸
C.井下爆破
D.矿井火灾
参考答案：A, B, C, D
-Which of these English CDs do you think I should buy, sir?
-__________ You're supposed to have ideas of your own.[ ]
A. It's up to you.
B. That's settled.
C. With pleasure.
D. I've got that.
对以下水质参数进行监测时，需在车间排放口采集水样的是（）
A、总磷
B、总汞
C、总铬
D、六价铬
