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问题 选择题
在正方体ABCD-A1B1C1D1中，已知AC=2
6
，则这个正方体内切球的体积为（　　）
A．12πB．9πC．4
3
π		D．4π
答案

∵在正方体ABCD-A1B1C1D1中，AC=2

6
，

∴设正方体的棱长为a，则

2
a=2
6
，解得a=2
3
．

因此，这个正方体内切球的直径2R=2

3
，解得R=
3
，

∴正方体内切球的体积为V=

4
3
πR3=
4
3
π•(
3
)3=4
3
π．

故选：C

完形填空
What do you think of the most important inventions in the world? The TV? The printing? The telephone? Or the computer? A report shows that they are not the only important inventions. Here are three other important inventions.
One of the simplest(最简单的) inventions is the toilet(冲水式马桶). Before toilets, waste ran into rivers from people’s houses. Illnesses were common in big cities, and it was often difficult to find clean drinking water.
Animal food is another important invention. Before the invention, most animals were killed（杀死） every autumn because there was not enough food for them in winter.  After hay (干草) became a kind of common animal food, animals could live through the long winter. The third great invention is glasses. Glasses help people read, write and do “close work” after the age of 45. Without glasses, the world would be difficult for the people above 45.
Inventions
Some most important inventions
Three other simple inventions
Before the inventions
The TV
The printing
The telephone
小题1:_______
The toilet
Waste ran into rivers from people’s house.
Illnesses were common in big cities.
小题2:It was often difficult to find ___________.
Hay /Animal food
People killed most animals in autumn because小题3:_________________
___________________ in winter.
小题4:_______
Reading, wrting and other “close work” would be difficult for the people 小题5:___________________________if there were not glasses.
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