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有人设计下列实验步骤，用氯化钠固体配制50g5%氯化钠溶液，其中不必要的是（　　）

化学上把“生成新物质的变化叫做化学变化”,下面对化学变化中“新物质”的解释，正确的是                                                           (    )

阅读下面短文，从A、B、C、D四个选项中选出最佳选项。

Where does the wind come from? What makes the wind move(移动) all the time? Scientists tell us that it is the sun. That makes air move, and makes it blow(吹). When the sun shines on the earth, it makes the earth hot. Then the earth makes the air hot. When the air becomes hotter, it also becomes lighter(更轻). The light air goes up. Cool air comes into take the place of（代替） the hot air. The hot light air goes up higher and higher until it becomes cool. Then it comes down again, and then the earth makes it hot again, and it has to go up. When the air move, it has wind.