用am，is，are填空。

1. Excuse me! ________ this your eraser?

2. What ________ those?

3. This ________ his ruler.

4. I ________ Mary. Are you Anna?

5. ________ these her English books?

6. Those ________ her pencils.

7. She ________ my sister.

8. He ________ my friend.

9. ________ those maps? No, they aren't. They are pictures.

10. These are your dictionaries. Here you ________.        

建立计算机网络的基本目的是实现数据通信和资源共享。计算机网络主要有以下四个功能：数据通信、资源共享、提高计算机的可靠性和可用性、 【2】 。