用所给词的适当形式填空。

1. I would like two _______ (bottle) of water.

2. We played with the baby. It _______ (is) fun.

3. I _______ (not) like apples.

4. _______ (this) are my parents.

5. They take a cab to _______ (they) hotel.

6. Danny _______ (break)his tail at the Palace Museum.

7. Jenny wants to buy _______ (gift)for her family.

8. Danny learns to ________ (fly) a kite.

9. This postcard _______ (have) a panda on it.

10. I can write _______ (a) e-mail.

如图4所示，细杆的一端与小球相连，可绕过O点的水平轴自由转动，细杆长0.5m，小球质量为3.0kg，现给小球一初速度使它做圆周运动，若小球通过轨道最低点a处的速度为va＝4m/s，通过轨道最高点b处的速度为vb＝1m/s，g取10m/s2，则杆对小球作用力的情况

①．最高点b处为拉力，大小为24N

②．最高点b处为支持力，大小为24N

③．最低点a处为拉力，大小为126N

④．最低点a处为压力，大小为126N

A．①③

B．①④

C．②③

D．②④