A:often
B:sometimes
C:always
D:never
①要“逆”流而行
②联合你前后左右的人一起采用“人体麦克法”:即拉起手有节奏地一起喊:“后退!”
③如果摔倒,要侧身蜷蛐双胳膊在颈后交叉,护住后脑、两侧太阳穴及内脏
④一定要双脚站稳,抓住身边一件牢固物体
共价键
H﹣H
F﹣F
H﹣F
H﹣Cl
H﹣I
E(kJ•mol﹣1)
436
157
568
432
298
Progress so far has been very good. We are,________,confident that the work will be completed on time.