搜题请搜索小程序“爱下问搜题”
问题 选择题
如图所示，AB是一质量为m的均匀细直杆，A端靠在光滑的竖直墙壁上，B端置于水平地面上，杆身与竖直方向夹角为θ，杆与地面的摩擦系数为μ，保持平衡，则此时杆与地面的摩擦力为（　　）

A．mgtgθ

B．mgsinθ

C．μmg

D．μmg

答案

答案：A

选择题

由于美国是世界上最大的资源消耗国，石油的用量猛增，会引起的环境问题是

①全球气温上升②臭氧层空洞扩大③地方病增多④排放CO2增加[     ]

A．①②

B．③④

C．②④

D．①④
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改错题
短文改错（共15小题；每小题1.5分，满分15分）
此题要求改正所给短文中的错误。对标有题号的每一行作出判断：如无错误，在该行右边横线上画一个勾(√)；如有错误(每行只有一个错误)，则按下列情况改正：此行多一个词：把多余的词用斜线(＼)划掉，在该行右边横线上写出该词，并也用斜线划掉。此行缺一个词：在缺词处加一个漏字符号(Λ)，在该行右边横线上写出该加的词。此行错一个词：在错的词下划一横线，并在该行右边横线上写出改正后的词。
注意：原行没有错的不要改。
One Sunday morning, Li Ming and his grandpa were feeded a
1. __________
bird in the cage. The bird was unhappy because it had enough food
2. __________
and waters. Li Ming didn’t know why.
3. __________
   The next morning on his way to the school, Li Ming saw some
4. __________
birds fly in the sky. Then he thought of the lonely bird in the cage.
5. __________
He decided to persuade his grandpa set the bird free. When he
6. __________
got home, he said to his grandpa, “Birds also need friends!” With
7. __________
his delight, his grandpa agreed him.
8. __________
    The bird was set free. Grandpa and the children were very
9. __________
happy to look the bird flying away into the sky.
10. __________
 
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