问题
单项选择题
材料的比强度是（）。
A.两材料的强度比
B.材料强度与其表观密度之比
C.材料强度与其质量之比
D.材料强度与其体积之比
答案
参考答案：B
搜题请搜索小程序“爱下问搜题”
材料的比强度是（）。
A.两材料的强度比
B.材料强度与其表观密度之比
C.材料强度与其质量之比
D.材料强度与其体积之比
参考答案：B
We sometimes call the lion “the king of the jungle (丛林)” because it is stronger and more dangerous than other animals. It can run faster than many animals and it can hunt (捕猎) the best. It is the highest animal in the 21 food chain (食物链).[ In the sea, the shark is one of the animals at the 22 of the food chain. It can swim faster than most other sea animals, and it can use its big teeth to eat them. What is at the top of the world’s food chain? 23 are! We are not the biggest or fastest, but we are the 24 We could not run faster than cheetahs (猎豹), so we 25 cars and now we can move the fastest. We could not 26 better than lions, so we invented guns (枪). Now we can hunt the best. People’s inventions are clever, but they can be dangerous, too. For example, people invented 27 , and now they make the air and rivers dirty. This can make 28 changes. Dirty rivers kill fish. Then bears cannot eat the fish and the bears die. If we kill one part of the food chain, 29 also die. Remember that we are a part of the food chain, so we are in danger too! If we protect animals, we are protecting 30 ! We should and we could do something for the world!
|