C

    Hi! I'm Alan. This is my dream house (梦幻屋). It has a small but nice room. Some pictures are on the wall. There is (有)a bookcase in my room. There is a desk and a chair in it. My schoolbag is on the desk. Oh! Where is my pencil case? It is under the chair. There are some pencils and a ruler in the pencil case. My shoes and a basketball are under the bed. I like my dream house very much.

化学符号是学习化学的重要工具。
（1）用化学用语(化学符号)表示：①一个硫酸根离子____；②五个银原子____ 。
（2）写出下列符号中数字的意义：①3Cl^-____；②____ 。

    Do you like to shop on the Internet? Things online are very cheap. I often get 1 online. Let me tell you how to buy one when I want to know something about a book. Firstly, I write an e-mail to the online shop. Then they will2me some pictures of the book. I think this is very helpful.

    Online shops are3open. I can do shopping even at midnight if I want to . Real shops usually close4 nine o'clock in the evening.

    After you5the online shopkeeper what you want, you can have your things in a few days. When you go shopping in a shopping mall, you have to talk 6 with the shopkeeper and walk a lot. I don't like it, because I get tired 7.

    I am teaching my grandmother8 online. She cannot walk very far(远).9it is easy for her to shop online. My brother wants to learn how to do it too. He is very10most of the time. When he has a little free time, he can shop online. So you see, shopping online saves time.

如图所示，绝热气缸A与导热气缸B、C均固定于地面，由刚性杆连接的绝热活塞与AB两气缸间均无摩擦，真空气缸C与气缸B通过阀门相连，气缸C的体积为2V₀，气缸A、B内装有处于平衡状态的理想气体，气体体积均为V₀，温度均为T₀，现打开阀门，等达到稳定后，A中气体压强为原来的0.4倍，设环境温度始终保持不变．求：