A: What do you ____ Halloween?

B: It's on October 31.

A: Yes. But do you know what people do on that day?

B: Of course. They ____ and dress up.

A: I hear that children love Halloween best.

B: Yes. Because they can play a game called “trick or treat” then.

A: How do they do that?

B: They paint their faces, ____ their neighbours' doors and shout “trick or treat”. If people don't give them any candy, they usually ____ them.

A: That's really interesting. Do people have a party on Halloween?

B: Yes, usually in the evening. People ____ and enjoy nice food.

①因为直线是无限的，所以平面内的一条直线就可以延伸到平面外去；

②两个平面有时只相交于一个公共点；

③分别在两个相交平面内的两条直线如果相交，则交点只可能在两个平面的交线上；

④一条直线与三角形的两边都相交，则这条直线必在三角形所在的平面内．

等腰三角形的一边为4，另一边为9，则这个三角形的周长为（　　）

如图所示，一个单匝矩形线圈水平放在桌面上，再线圈中心上方有一竖直的条形磁体，此时线圈内的磁通量为0.05Wb．在0.5s的时间内，将该条形磁体从图示位置竖放到线圈内的桌面上，此时线圈内的磁通量为0.10Wb．试求此过程：

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