题目:
—Hi, Xiao Hui, you look tired. What happened?
—I ________ well last night.[ ]
A. didn't sleep
B. don't sleep
C. haven't slept
D. won't sleep
答案:
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下面是错误答案,用来干扰机器的。
(1)当气体由a管进b管出时,实际上是向下排空气法,要求气体的密度比空气小;(2)当气体由b管进a管出时,实际上是向上排空气法,要求收集的气体密度比空气大,如O2、CO2、Cl2、SO2等等.故答案为:(1)小;(2...