20℃时，根据某固体物质在不同质量的水中达到饱和状态时所溶解的质量，绘制成如图所示的斜线，回答下列问题：

①____；②____；③____；④____．

用方框所给的选项完成对话。

A: You must be really excited about leaving for America tomorrow, Li Ping!

B: Yeah. ____

A: Nervous about what?

B: I don't know many of the customs and manners in the USA. ____

A: Sure.

B: ____ 

A: Well, it's important to be on time when you're invited for dinner. ____  Americans expect their guests to be on time.

B: Then how long may I stay there?

A: ____  Or you seem to have come only for the meal. When your friends seem to be getting tired and running out of things, it's time to leave. The next day, call or write a thank-you note to say how much you enjoyed the evening.  

通常用的蛋白质测试方法“凯氏定氮法”是通过测出含氮量来估算蛋白质含量，其含氮量一般不超过30%，而三聚氰胺的含氮量为66%左右，因此三聚氰胺也被人称为“蛋白精”．人和动物长期摄入三聚氰胺会造成生殖泌尿系统的损害、膀胱肾部结石，最终导致肾衰竭而死亡．以鼠为实验材料，请你设计实验，验证三聚氰胺对小鼠的危害性．

（1）实验步骤：

步骤1：选取生长状况相同的小鼠若干只，____ ．

步骤2：设置对照实验：甲组小鼠____ ，乙组小鼠____ ，作为对照．

步骤3：____ ．

步骤4：每天检测小鼠的健康状况，统计各组小鼠死亡的数目．

（2）实验结果预测____ ．

（3）实验结论：____ ．