A.    B.        C.        D.   

3.在某星球上，宇航员用弹簧秤称得质量为m的砝码重量为F，乘宇宙飞船在靠近该星球表面空间飞行，测得其环绕周期为T，根据上述数据，得出该星球的质量为

D．物体滑行的总时间为2.5s

A．物体与水平面间的动摩擦因数为0.25

B．物体克服摩擦力所做的功为 -50J

C．物体滑行的总时间为4s

2．质量为1kg的物体以某一初速度在水平面上滑行，由于摩擦阻力的作用，其动能随位移变化的图线如图所示，g取10m/s2，则以下说法中正确的是

1.如下图所示，小球从高处下落到竖直放置的轻弹簧上，在将弹簧压缩到最短的整个过程中，下列关于能量的叙述中正确的是

A．重力势能和动能之和总保持不变。

B．重力势能和弹性势能之和总保持不变。

C．动能和弹性势能之和总保持不变。

D．重力势能、弹性势能和动能之和总保持不变。

85. the→a。冠词的错误。这里表示“一个更好的地方”，用a better place而不是“那个更好的地方”；注意后面的place to live是正确的，可以将掉尾介词in省略。

书面表达范文：

   There’s a lot of talk in my class about whether the senior 3 students should spare the time to take part in the winter long run program. 60% of the students think it a good idea, which can require us to take exercise every day. Besides running, we can do many sports such as morning exercises, playing ping-pong ball and playing basketball, but it shouldn’t take up too much time. Exercise builds one’s body and reduces diseases. Sports let their brains have a rest so that their revision will be more effective.

   On the other hand, 30% believe taking exercise is a waste of time and tiring. After having sports, they are much too excited for a long time to pay attention to their lessons. It’s also possible to be hurt in sports.

   As far as I’m concerned, I think it necessary for us to take some exercise. After some exercise, we can feel more refreshed and relaxed, which can help us learn better.

84. but→and连词的错误。这里表示顺接和递进关系，用连词and而不是but。

83.by删除。从句子结构看，这里的v.-ing结构做句子主语，应该将介词删除。

82. cup→cups。名词的错误。用复数名词cups表示泛指。