从所给出的单词中选出合适的完成对话。

supermarket     meat     shopping    rainy    tomatoes

 Tom: Mum, there's no food at home. Let's go ____today.

Mum: But how's the weather?

 Tom: It's a sunny day. It's not____

Mum: OK. Is there any____in the kitchen?

 Tom: No, there isn't.

Mum: Are there any ____or potatoes?

 Tom: There aren't any potatoes but there is only one tomato.

Mum: All right. Let's go to the ____now.

分析字形：“晒”

人的性别由性染色体决定，女性体细胞的性染色体组成是（　　）

如图2—3—4所示洋葱根尖细胞分裂过程中染色体的变化，据图回答：

(1)写出下列标号所代表的结构的名称：

    ①____ ；②____ 。

(2)试说明分裂前后，细胞内②的数目是否有变化?这对细胞的生活有什么意义?____ 。