如图甲所示，水平地面上的一物体受到方向不变的水平拉力F的作用，F的大小与时间t的关系及物体速度v与时间t的关系如图乙、丙所示．则下列说法不正确的是（　　）

A．0～2s内物体处于静止状态

B．4～6s内物体的机械能不变

C．2～4s内物体受到的摩擦力为3N

D．4～6s内拉力对物体做功的功率为8W

根据句意及首字母提示填写单词。

1. Now some students begin to think of how to spend the coming winter v______.

2. Don't t________ the paper everywhere on the street.

3. Tom was so pleased that I a___________ his birthday present.

4. I'm not kidding. It's s_______.

5. I can't come in because I can't find my k________ to the door.