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问题 选择题
如图所示，两根相距为l的平行直导轨ab、cd、b、d间连有一固定电阻R，导轨电阻可忽略不计；MN为放在ab和cd上的一导体杆，与ab垂直，其电阻也为R；整个装置处于匀强磁场中，磁感应强度的大小为B，磁场方向垂直于导轨所在平面（指向图中纸面内）；现对MN施力使它沿导轨方向以速度v（如图）做匀速运动；令U表示MN两端电压的大小，则（　　）

A．U=vBl，流过固定电阻R的感应电流由b到d

B．U=vBl，流过固定电阻R的感应电流由d到b

C．U=vBl，流过固定电阻R的感应电流由b到d

D．U=vBl，流过固定电阻R的感应电流由d到b

答案

答案：A

完形填空
完形填空。
     Mary is   1   American girl. She is now in Beijing with her parents. It's Sunday morning. Mary gets up
early. After breakfast her parents   2   the zoo. They want to see the panda and other animals. The panda
lives only   3  . There are   4   pandas in America.   5   they like the panda best. Outside the zoo gate there
is a picture. It's a picture of a panda   6   "welcome". The panda is round and fat. It   7   a ball. It moves
like a ball rolling (滚动). The elephant is the biggest ainimal   8  . There are many monkeys on the hill. Some
of them are sitting   9   the trees.Some are picking nuts. And  10  are running or climbing up the trees.
( )1.A.an          
( )2.A.get her to  
( )3.A.in America  
( )4.A.no any      
( )5.A.So          
( )6.A.in          
( )7.A.looks       
( )8.A.in land     
( )9.A.on          
( )10.A.the other    		B.a            
B.take her to   
B.in England   
B.not a        
B.And          
B.with         
B.look like   
B.on the land     
B.in           
B.the others    		C.the           
C.take she to    
C.in China      
C.any           
C.But           
C.on            
C.looks like    
C.in the land   
C.at            
C.other          		D./              
D.bring her to                 
D.in Canada      
D.not any        
D.Because        
D.at             
D.looks at       
D.on land        
D.for            
D.some         
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选择题
若
C2n
A22
=42，则
n!
3!(n-3)!
的值为（　　）
A．6B．7C．35D．20
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