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.

如图是某同学所画的自制简易净水器示意图．

（1）制作材料：见图标注，则a是____ ，b是____．

（2）使用说明：使用一段时间后，有关物质吸附杂质已达饱和．这时清洗后可以继续使用的是纱布、石英砂和____ ，需要更换的是膨松棉和____．

①物体的形状    ②材料    ③材料之间的联接方式    ④物体重心的位置

—It ____________ like a small mouse.