A.    B.        C.        D.   

3.在某星球上，宇航員用彈簧秤稱得質量為m的砝碼重量為F，乘宇宙飛船在靠近該星球表面空間飛行，測得其環(huán)繞周期為T，根據(jù)上述數(shù)據(jù)，得出該星球的質量為

D．物體滑行的總時間為2.5s

A．物體與水平面間的動摩擦因數(shù)為0.25

B．物體克服摩擦力所做的功為 -50J

C．物體滑行的總時間為4s

2．質量為1kg的物體以某一初速度在水平面上滑行，由于摩擦阻力的作用，其動能隨位移變化的圖線如圖所示，g取10m/s2，則以下說法中正確的是

1.如下圖所示，小球從高處下落到豎直放置的輕彈簧上，在將彈簧壓縮到最短的整個過程中，下列關于能量的敘述中正確的是

A．重力勢能和動能之和總保持不變。

B．重力勢能和彈性勢能之和總保持不變。

C．動能和彈性勢能之和總保持不變。

D．重力勢能、彈性勢能和動能之和總保持不變。

85. the→a。冠詞的錯誤。這里表示“一個更好的地方”，用a better place而不是“那個更好的地方”；注意后面的place to live是正確的，可以將掉尾介詞in省略。

書面表達范文：

   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連詞的錯誤。這里表示順接和遞進關系，用連詞and而不是but。

83.by刪除。從句子結構看，這里的v.-ing結構做句子主語，應該將介詞刪除。

82. cup→cups。名詞的錯誤。用復數(shù)名詞cups表示泛指。