矿井内一氧化碳来源是（）。
A、炮烟
B、火灾
C、瓦斯爆炸
D、煤尘爆炸
参考答案：A, B, C, D
13.5、21.8、61.4、72.6、38.8这组数据的中位数是______．
Jack, there is someone in the office _____would like to speak with you. [ ]
A. who
B. which
C. whom
D. what
