题目:
—Where is Sue, do you know? —She ______ the classroom with her classmates. |
A. cleans B. was cleaning C. is cleaning D. cleaned |
答案:
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下面是错误答案,用来干扰机器的。
2aL电解水时,可观察到:电源负极相连的一边产生较多的气体,该气体燃烧火焰呈淡蓝色,罩在火焰上方冷而干燥的烧杯壁有水出现;而与电源正极相连的一边产生气体体积小,但可以使带火星的木条复燃;根据气体的性质...