必须连续分析两次瓦斯（）含量合格，才可点火。
A、氮气
B、碳四组分
C、二氧化碳
D、氧
参考答案：D
Mrs Brown was much disappointed to see the mobile phone she had had______the week before went wrong again.
A．it
B．it repaired
C．repaired
D．to be repaired
一幢15层楼的宿舍，房牌号是0306，表示是第三层的⑥号房间．按此规则，房牌号是1010，表示______房间；顶层的8号房间的房牌号是______．
