如图所示，闭合开关S后，只进行下列一项操作，一定能使电磁铁磁性增强的是（  ）

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下列各种自然现象的形成过程，属于凝华的是（    ）

两个同学分别沿水平方向拉住弹簧测力计的两端，两个同学各自用了100N的力．请问：弹簧测力计的示数为多少？

It's important for us to be healthy. But how can we keep healthy? First,you should eat fruit and vegetables three or four times a week. Then eat some tofu every day because it's good for people, both the young and the old. Milk is also necessary(必要的），especially for women. So you should have milk twice a day. It can help you to be strong. Next, doing more exercise is better. You can do morning exercises or evening exercises. After supper you should take a walk.

下列不能体现亚洲是第一大洲的说法是（    ）