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问题 问答题

从一定高度的气球上自由落下两个物体，第一物体下落1s后，第二物体开始下落，两物体用长93.1m的绳连接在一起．问：第二个物体下落多长时间绳被拉紧？

答案

设第二个物体下落ts后绳被拉紧，此时两物体位移差△h=93.1m

△h=

1
2
g(t+1)2-
1
2
gt2，

即93.1=

1
2
g(2t+1)，

解得　 t=9（s）

答：第二个物体下落9s绳被拉紧．

完形填空

Dear friends,

I am a wolf from the north. I live in the w  小题1:  . And I am quite sad.

I live in a family group with my parents. We are friendly t  小题2:   each other and we look after each other. We can see, hear and smell things far a  小题3:  . We are good at hunting, but we never k 小题4:   for fun.

We used to live a happy life. But s  小题5:   , we have some serious problems now. Some people came last month and they destroyed(摧毁) a lot of forests. They wanted to build a highway. We lost many l  小题6:   areas. We had to move. But when we had a new home, people followed us and they cut down more trees. This time, they wanted to make the forest into farmland. As a r 小题7:  , we had to move again, but things didn’t get better. People came again and hunted us. They thought we were dangerous to h 小题8: . If people keep doing like this, it will l  小题9:    to fewer and fewer wolves in the world.

We are now in d 小题10:  . What can we do? Please save us!
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单项选择题

中国的姓氏有一个非常大的特点，那就是同是一个汉族姓氏，却很可能有着非常大的血缘差异。总体而言，以武夷山——南岭为界，中国姓氏的血缘明显地分成南北两大分支。两地汉族血缘差异颇大，甚至比南北两地汉族与当地少数民族的差异还要大。这说明随着人口的扩张，汉族不断南下，并在2000多年前渡过长江进入湖广，最终越过海峡到达海南岛。在这个过程中间，南迁的汉族人不断同当地说侗台、南亚和苗族语的诸多少数民族融合，从而稀释了北方汉族的血缘特征。
以下哪项如果为真，最能反驳上述沦证

A．南方的少数民族有可能是更久远的时候南迁的北方民族。
B．封建帝王曾经敕封少数民族中的部分人以帝王姓氏。
C．同姓的南北两支可能并非出自同一祖先。
D．历史上的确也曾有少数民族北迁的情况。
E．不同姓的南北两支可能出白同一祖先。
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