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油菜花的花从结构上是( ) A.细胞 B.组织 C.器官 D.系统
1年前
在一定条件下,同一反应进行的快慢与反应物的浓度成正比.用100g 30%的硫酸与少量镁粉反应,为了使反应慢点而不影响生成氢气的质量,可向所用硫酸中加入的物质是 [ ]
1年前
Traffic lights are very important for us.
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There is a(an) ______ that more graduates choose teaching as their permanent careers.
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It's eight o'clock. It's time for ________ now.
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