史前社会人类面临的环境问题有( )
①洪水 ②猛兽 ③风暴 ④废气
A:①②③
B:①②④
C:①③④
D:②③④
算式42-42÷6的结果是0。____
一 How long have you ?
— For three days.
— For about half a month.