矿井主要通风机装置外部漏风率有提升设备时不得超过（）。
A.5％
B.10％
C.15％
D.20％
参考答案：C
设α：1≤x≤2，β：m≤x≤2m+3，m∈R，α是β的充分条件．求m的取值范围．
Is this your necklace, Mary? I____ it when I was cleaning the bathroom this morning.
A．came across
B．dealt with
C．looked after
D．went for
