A:
B:
C:
D:
①将矿井中的氧气抽出;
②加强安全管理,杜绝明火源;
③提高通风能力;
④降低瓦斯气体的着火点.
Is that _________ computer game?
过点(﹣2,0)的直线l与抛物线y=x22相交于两点,且在这两个交点处抛物线的切线互相垂直,则直线l的斜率k等于( )
—It's too late. I have to go now. —Oh, it's raining heavily outside. You'd better stay ___________ it stops.