鼓风机是利用动能转换为（），实现空气的排出的。（A）势能 （B）电能 （C）压能 （

根据短文内容，回答问题。

      It's sunny today. My friends and I are playing on the beach (沙滩). It's a very beautiful place (地方). The

water is clean and blue. We are having a good time. Many birds are flying over the sea. Some are standing on

the rock (岩石). Many people are swimming. Some boys are playing football. Some people are lying (躺) on

the beach. Mary is sitting on a chair and drawing a picture. John is taking pictures of his friends. And I'm

sitting on a rock and writing to you! What are you doing now? I hope I can get your letter soon.

　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　Best wishes,

　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　Tim

1. What's the weather like today?

__________________________________________________________

2. Where are Tim and his friends?

__________________________________________________________

3. Can they see birds?

__________________________________________________________

4. Is Tim playing football on the beach?

__________________________________________________________

5. What is John doing?

__________________________________________________________

数列{a_n}中，a₁=1，且点（a_n，a_n+1）在直线l：2x-y+1=0上．

（Ⅰ）设b_n=a_n+1，求证：{b_n}是等比数列；

（Ⅱ）设C_n=n（3a_n+2），求{C_n}的前n项和．

离子反应、复分解反应、置换反应、氧化还原反应之间可用集合关系来表示，其中正确的是 [ ]

A.

B.

C.

D.

Lucy knew nothing about it _____ her sister told her.[ ]

A. because

B. until

C. if

D. since

汽车的故障可分为轻微故障、一般故障、严重故障和（）故障。

A.功能

B.参数

C.报废

D.致命