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问题 多选题

一轻杆一端固定质量为m的小球，以另一端O为圆心，使小球在竖直平面内作半径为R的圆周运动，则[ ]

A.小球过最高点时，杆所受弹力可以为零

B.小球过最高点时的最小速度是

C.小球过最高点时，杆对球的作用力可以与球所受重力方向相反

D.小球过最高点时，杆对球的作用力一定跟小球所受重力的方向相反

答案

AC

多项选择题

中药材的含水量过高时会发生

A．软化

B．生虫

C．走味

D．潮解

E．霉变
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填空题
用方框里适当的短语完成句子。
in addition to   a lot of   be famous   hear of  of course 
prefer...to  like  now and then   all the time   not only...but also
1. The dancers are good at _____ different music.
2. The young violinist plays the guitar _____the violin.
3. The star _____ for rock music in the world.
4. _____do the people sing classical songs _____they sing pop songs.
5. Lots of young fans likes pop _____.
6. We haven’t seen the small country or _____ it.
7. The singers use modern drums and _____ use guitars.
8. I    playing the piano _____ playing the violin.
9. —Would you like to go to the concert?
    —_____，I'd like to.
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