From the earlier time it was well 1 to the Peruvians that when a cut 2 made in the thick s

From the earlier time it was well 1 to the Peruvians that when a cut 2 made in the thick skin of a 3 tree, a white liquid like milk came 4 . From this fluid (流动的) a sticky 5 of rubber might be made. This rubber is 6 and wax-like when warm so that it is 7 to give any form.
The Peruvians 8 the discovery that it is very good for 9 out water. Then in the early 10 of the century they made overshoes to 11 their feet dry. Then a certain Mr Mackintosh 12 coats of cloth which were 13 with rubber. Today Mackintosh raincoats are still 14 after him.
But these first rubber shoes 15 raincoats were unpleasantly soft and sticky in 16 . They were also stiff and very 17 in winter. They were like wax(蜡) although they 18 a bit stronger.
But the rubber 19 use today has been improved. It is 20 sticky but soft and elastic(弹性的) and strong enough for any season.
1. A. talked B. heard C. seen D. known
2. A. has B. was C. may D. will
3. A. rubber B. apple C. orange D. oak
4. A. from B. through C. out D. up
5. A. raincoat B. shoes C. border D. mass
6. A. hard B. fast C. stubborn D. soft
7. A. important B. impossible C. possible D. uncertain
8. A. made B. found C. wrote D. neglected
9. A. finding B. keeping C. making D. pouring
10. A. kind B. part C. sort D. halves
11. A. clean B. clear C. keep D. prevent
12. A. made B. found C. appeared D. gave
13. A. full B. like C. lined D. applied
14. A. looked B. named C. made D. searched
15. A. or B. and C. with D. but
16. A. today B. summer C. winter D. rain
17. A. soft B. sticky C. elastic D. cold
18. A. felt B. made C. needed D. produced
19. A. Mr Mackintosh B. the Peruvians C. we D. is
20. A. also B. always C. neither D. not1-5DBACD 6-10DCABB 11-15CACBB 16-20BDACD

(答案→)1-5DBACD 6-10DCABB 11-15CACBB 16-20BDACD 解析： 本文是一篇说明文，讲叙橡胶的产生、特点和作用。1. D。be well known 是固定短语，表示“对…了解、熟悉”。2. B。因为“切口(cut)”可知应该是被人去做，所以是 was made。3. A。根据下文两次出现的 rubber 可得出答案。4. C。从上文可以得知“像牛奶一样的白色液体从橡胶树上流出来”。5. D。从上下文可以得知“从树上流下来的液体，慢慢会变稠”，所以“粘团”就形成了，但它不能直接形成雨衣或鞋。6. D。根据常识橡胶是“软的”。7. C。根据前面的形容词 warm 得出答案，当变暖或加热时“能”做出任何形状。8. A。因为“发现”是名词，不能选found，make a discovery是固定短语。9. B。根据常识，橡胶可以“防”水，其余选项不符句意。10. B。表示本世纪的“早期、前期”，不能选 halves，如果用 half不能用复数。11. C。根据前面的“鞋垫”和后面的“干燥”得出答案是“保持干燥”。12. A。根据后面的 coat 判断答案是“被做”。13. C。指这种布料(cloth)是用橡胶“排制”而成的。14. B。根据前面的雨衣判断可知仍然还是以他的名字“命名的”，其余选项不符句意。15. B。根据句意，这是两个物质名词 shoes 和 raincoat 是并列的，但不能选or(或者)。16. B。夏天天气炎热，雨衣变软，故 summer 符合语境。17. D。根据常识，橡胶在夏天温度高时变软，相反在冬天“冷”时变硬。18. A。根据前面的“像蜡”和后面的 stronger 得出答案是“摸起来”，表示感觉。19. C。根据句中的时间状语 today 判断是 we(我们)使用。20. D。根据两个相反的形容词，得出答案(not…but意为“不是…而是”)。

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这下我知道了

解：（1）火箭在加速上升过程中，质量不变，速度变大，故其动能变大；同时质量不变，高度变大，故其重力势能变大，故其机械能变大；该过程中消耗了燃料所释放的内能，产生了机械能，故是将内能转化为机械能的过程；由于地球在自西向东不停地自转，故利用惯性的知识，火箭在升空后应向偏东一些的方向飞行能节省燃料；
（2）载人飞船与运载火箭成功分离前，载人飞船和运载火箭是一体的，即运动的速度相同，所以飞船相对于火箭是静止的；
太空中没有空气，声音不能传播，故卫星只能通过电磁波与地面联系．
（3）卫星对月定向姿态变轨，即其运动的状态发生了改变，即说明力可以改变物体的运动状态；同时太阳能电池工作时，其消耗了太阳能，产生了电能，故是将太阳能转化为电能的装置．
故