循环风有何害处?
参考答案:
(1)掘进工作面有毒有害气体和粉尘浓度会越来越大,使作业环境恶化;
(2)由于风流中的瓦斯浓度不断增加,当其进入局部通风机时,极易引起瓦斯爆炸。
已知(x+1)2+|y-1|=0,求2(xy-5xy2)-(3xy2-xy)的值.
Try on this red skirt; you will look great _____ it. [ ]
A. on
B. by
C. in
D. for