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.

为探究物质对草履虫的刺激是有利还是有害，某中学生物兴趣小组的同学做了以下实验：（1）取两片载玻片，分别编号1和2．（2）在每片载玻片上滴加两滴相同的草履虫培养液，用解剖针在1、2号载玻片的两个液滴之间轻轻地画一下．（3）用显微镜观察培养液中的草履虫．

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