矿井应按规定进行矿井瓦斯等级和（）涌出量鉴定工作。
A.氧气
B.二氧化碳
C.氮气
D.氢气
参考答案：B
Mary is as fast as, if not faster than, anyone in her class and should be on the team.
A．as fast, if not faster than, anyone else
B．as fast as, if not more fast than, anyone
C．as fast as, if not faster than, anyone else
D．as fast, if not faster than, anyone
圆心确定圆的______，______确定圆的______．
