( 1 )用天平测出雨花石的质量m₁；

( 2 )用天平测出空烧杯的质量m₂；

( 3 )在溢水杯中____，将雨花石轻轻放入溢水杯中浸没，并同时用烧杯收集从溢水杯中溢出的水，用天平测出烧杯和水的总质量m₃；

( 4 )设水的密度为ρ，则此雨花石的密度表达式为ρ_石=____．（用m₁、m₂、m₃，ρ表示）

发源于西欧的启蒙运动能迅速波及欧洲大多数国家的主要原因是

阅读理解，判断正误。

Bill and Ben are shopping.

Bill: There is a store. Let's go in.

Ben: Let's go.

Assistant: Can I help you?

Bill: Yes, do you have any shoes?

Assistant: Yes, we do. What size do you want?

Bill: Size 21, please.

Assistant: Here you are.

Bill: Oh, this shoe is just right for my left foot. But this one is too big for my right foot.

Assistant: You can try this pair on. They are size 20.

Bill: Oh, this time my right foot is all right. But this shoe is too small for my left foot.

Assistant: What size do you want?

Bill: I don't know. Can you give me an idea?