矿井下沼气浓度达到（）时，就有发生爆炸事故的危险。
A.1～4％
B.5～16％
C.20％以上
参考答案：B
I asked Danny to _____ me my book, but he brought me his book. [ ]
A. take
B. fetch
C. carry
D. match
加强基层保卫工作，要坚持打击为主，综合治理.
