井下二氧化碳的来源有()
A.爆破工作和瓦斯煤尘爆炸,煤和坑木氧化
B.煤岩(岩)层中渗出、突出或喷出
C.碳酸性岩石与酸性水分解
D.人员呼吸
参考答案:A, B, C, D
—I called you but you didn’t reply to me yesterday.
—Oh, sorry, I ________ Dad, where are we going?(《爸爸去哪儿》)at the cinema.
A.was watching
B.have watched
C.was watched
D.had watched
客流调查的形式有综合调查、节假日调查和日常调查三种。一般以节假日调查为主。