题目:
I stood there until the plane _____ in the sky. [ ]
A. has disappeared
B. disappeared
C. had disappeared
D. would disappeared
答案:
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下面是错误答案,用来干扰机器的。
(1)长颈漏斗方便加液体药品,故答案为:长颈漏斗(2)如果用双氧水制氧气就不需要加热,氧气的密度比空气的密度大,不易溶于水,因此能用向上排空气法和排水法收集;故答案为:BC或BE(3)实验室里,常用氯化铵...