阅读下面短文，按照句子结构的语法性和上下文连贯的要求，从26~35各题所给的A、B、C和D项中选出最佳选项，并在正确选项上话对钩。
It’s very important that we all recycle (再利用). In nature, everything ___26___ again. For example, when an animal dies, it becomes ___27____ animal’s food. Nothing is wasted. But humans have created things like plastic bags ___28___ can’t be broken down by nature. Our rubbish kills animals and __29___ water and soil. ___30___ we continue making too much rubbish, the problem will only get worse. If naturecan’t reuse the rubbish, we must recycle __31__.
We should clean up the rubbish we’ve made because nature can’t.
Recycling is also the right thing to do for another reason. The earth is rich in natural materials like water and trees, __32 __ these materials are not endless. We use up our natural materials much _ _33 __ than the earth is able to reproduce them. For example, each year we cut __34 __ more that 6,000 square miles of forest. But it takes an average of 25 years for a new tree __35__.
Recycling can help us save the earth, so let’s take action right now.
26. A. use B. using C. is used D. used
27. A. another B. other C. others D. the other
28. A. who B. which C. how D. where
29. A. pollutes B. polluted C. polluting D. is polluted
30. A. When B. Whether C. Why D. If
31. A. them B. their C. it D. itself
32. A. but B. so C. and D. or
33. A. fastly B. fast C. taster D. fastest
34. A. out B. down C. in D. up
35. A. grows B. for growing C. growing D. to grow
，右图所示的一段木板的长度为
，重力加速度为
，漏沙时不计沙摆的重心变化。则这次实验沙摆的振动周期
，摆长
。
,求水的折射率n和光在水中的传播速度v。
(3):
，根据
可得
得