制作人体口腔上皮时，需要滴加生理盐水，并在生理盐水中涂抹开来，请问将口腔上皮细胞置于生理盐水中的目的是什么（  ）

①主要矛盾与次要矛盾在一定条件下相互转化

②矛盾的次要方面和矛盾的主要方面在一定条件下相互转化

③事物的质变必定由量变引起

④量变必然引起质变

根据短文，从A、B、C、D四个选项中选择正确答案填空。

    It's December 28th. New Year's Day is 1. Ma Li is in a 2 shop. She wants to buy a blouse 3 her mother. She is happy because she 4 a blue blouse. It looks pretty. She thinks it 5 her mother's trousers well, so she asks the shopkeeper what the 6 is. “198 yuan,” says the shopkeeper. Ma Li is surprised (吃惊的), “Too 7! What's it made of?” The shopkeeper tells her the blouse is made of silk. “Good things always 8 much,” he says.

  “But I have only 190 yuan. Can it be cheaper (更便宜)? I buy it for my mother. ”

  “9. 198 yuan is the last price. But I will lend you 8 yuan.”

  “10? We don’t know each other.”

  “Because I love my mother, too,” says the shopkeeper with a smile (微笑).

分子是构成物质的一种粒子，下列有关水分子的叙述正确的是（　　）