题目:
As for how to promote public education, Professor Li gave us a lot of suggestions which _____ reasonable and practical.
A.appeared
B.sounded
C.looked
D.listened
答案:
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答案:D题目分析:用化学方法除杂质有2个原则:1、所加的物质只能与杂质反应,2、在与杂质反应的时候,不能引入新的杂质, A、除去N2中O2,通过足量的灼热铜网,氧气会与灼热铜网反应生成归氧化铜,而氮气不会反...