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问题 选择题

西欧粮食收获量与播种量之比，据罗马时代《克洛米拉农书》记载为4——5倍，据十三世纪英国的《亨利农书》记载为3倍；而从《齐民要术》看，我国6世纪粟的收获量为播种量的24——200倍，麦 类则为44——200倍。这主要是因为 [ ]

A．中国古代科学技术领先世界    

B．中国古代农业的精耕细作技术发达

C．中国古代铁犁牛耕技术发达    

D．中国古代粮食的单位面积产量届世界领先地位

答案

答案：B

阅读理解

1.How many times did you brush your teeth yesterday?
·Finding：A full 33% of seniors brush their teeth only once a day.
·Step：Remove the 300 types of bacteria in your mouth each morning with a battery－operated toothbrush. Brush gently for 2 minutes, at least twice a day.
2．How many times did you wash your hands or bathe yesterday?
·Finding：Seniors, on average, bathe fewer than 3 days a week. And nearly 30% wash their hands only 4 times a day—half of the number doctors recommend.
·Step：We touch our faces around 3，000 times a day—often inviting germs(病菌)to enter our mouth, nose, and eyes. Use toilet paper to avoid touching the door handle. And, most important, wash your hands often with hot running water and soap for 20 seconds.
3．How often do you think about fighting germs?
·Finding：Seniors are not fighting germs as well as they should.
·Step：Be aware of germs. Do you know it is not your toilet but your kitchen sponge(海绵)that can carry more germs than anything else? To kill these germs, keep your sponge in the microwave for 10 seconds.
小题1:What is found out about American seniors?
A．Most of them have good habits.
B．Nearly 30% of them bathe three days a week.
C．All of them are fighting germs better than expected.
D．About one third of them brush their teeth only once a day.
小题2:Doctors suggest that people should wash their hands ________．
A．twice a day B．three times a day
C．four times a dayD．eight times a day
小题3:Which of the following is true according to the text?
A．We should keep from touching our faces.
B．There are less than 300 types of bacteria in the mouth.
C．A kitchen sponge can carry more germs than a toilet.
D．We should wash our hands before touching a door handle.
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计算题

如图所示，在光滑的水平面上有两个质量相同的球A和球B，A、B之间以及Ｂ球与固定点Ｏ之间分别用两段轻绳相连，以相同的角速度绕着O点做匀速圆周运动．

1）画出球A、B的受力图．

2）如果OB=2AB,,求出两段绳子拉力之比TAB:TOB
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