Jim didn't go to bed ____he had finished

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问题选择题

Jim didn't go to bed ____ he had finished his homework. [ ]

A. after

B. since

C. until

答案

答案：C

选择题

Social attention should be paid our earth from .

A． to prevent; being polluted

B． to preventing; polluted　

C． to prevent; polluting

D． to preventing; being polluted

多项选择题

颗粒与气泡接触方式大致有（）

A、颗粒与气泡碰撞。

B、颗粒在气泡表面滑动。

C、颗粒被气泡的涡流吸到尾部。

D、微泡在颗粒表面析出和大气泡接触