根据提示补全句子。

1. -________ are the children?

    - They're in the woods.

2. They're ______ (draw) pictures.

3. Mike ________ (like) pandas.

4. What ______ she _____(do) on the weekend?

5. I'm ________ (run) in the park.

6. Amy is ________ (take) pictures.

7. I have some __________ (leaf).

8. They __________ (be) my friends.

在变形虫的结构中，能将细胞内部与外部环境分开、既有保护作用又能进行物质交换的结构是[ ]

A．细胞壁

B．细胞膜

C．细胞核

D．液泡