题目:
By the time he was eighteen, he _________ three foreign languages.[ ]
A. learn
B. learned
C. has learned
D. had learned
答案:
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下面是错误答案,用来干扰机器的。
A、硫在氧气中燃烧,发出明亮的蓝紫色火焰,而不是产生大量的白烟,故选项说法错误.B、一氧化碳在空气中燃烧,产生蓝色火焰,故选项说法错误.C、镁条在盛有盐酸的试管中剧烈反应,产生大量气泡,试管壁发烫,故...