有一物体从静止开始自一定倾角的斜面顶点无摩擦往下滑动，下面哪个图象能正确表示物体加速度a、速度v的x分量a_x、v_x随时间变化的关系？（　　）

A．

B．

C．

D．

句型转换.

1. I have some story books. (改为否定句)

    I _________ have _________ story books.

2. Miss Wang likes playing sports every day. (改为一般疑问句)

    _________ Miss Wang _________ playing sports every day?

3. She often swims with her friends at the pool. (用now改写)

    She _________ _________ with her friends at the pool.

4. Tom is reading a book now. (画线部分提问)

     _________ _________ Tom _________ now?

5. She usually does homework at ten o'clock. (画线部分提问)

     _________ _________ she usually do homework?

6. Our school has twenty classes. (同义句改写)

     _________ _________ twenty classes _________ our school?

7. like, I, the, going, my, movies, to, with, friends. (连词成句)

    _________________________________________________