They didn't go to bed they finished their homework. [ ]
A.until
B.because
C.when
D.if
答案:A
按照《大气污染物综合排放标准》(GB16297-1996)中的规定,我国以控制无组织排放所造成的后果来对无组织排放实行监督和限制。
下列分子式分别代表什么物质。
CH4