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问题 多选题

如图所示，A、B为两个带等量正电的点电荷，O为A、B连线的中点．以O为坐标原点、垂直AB向右为正方向建立Ox轴．下列四幅图分别反映了在Ox轴上各点的电势φ和电场强度E随坐标x的变化关系，其中可能正确的是（　　）

A．

B．

C．

D．

答案

等量正电荷连线的中点电场强度为零，沿x轴方向无穷远处电场强度为零，知电场强度沿x轴方向先增大后减小．等量正电荷的电场线是排斥状的，x轴上沿正方向，因为沿电场的方向电势逐渐降低，知电势随x逐渐降低，电势与x图线的斜率表示电场强度的大小，知斜率先增大后减小．故B、C正确，A、D错误．

故选BC．

完形填空
完形填空.     

          One day a very rich family in Guangzhou went on a trip to the
countryside. The father wanted to show his son how   1 people lived,so
they spent a day and a night 2 the farm of a very poor family. When they
got back froru   their      3,   the   father asked his son, “ My dear son, how
was the trip?”      
       “Very good , Dad !”      
       “Did you see how poor people lived?”the father asked.      
         “Yeah!”
       “And   4   did you learn?”       
         The son answered, “We have a dog at home, and they have four. We
have a pool that reaches to the middle of the garden and they have a creek
that has   no     end. We have very expensive  5   in the garden and they have
the stars. Our patio reaches to the front yard,yet they have the whole
horizon. "     
           6   the little boy finished,his father was speechless.      
         His son added,"Thank you for   7  me how poor we are ! "  
         8  it true that it all depends on the way you look at things? Attitude
is   9   !It's very   10   to make a decision to have a good and positive
attitude every day !

( )1. A.many        
( )2. A. in          
(     )3. A. trip        
(     )4. A. who        
(     )5. A. flowers    
(     ) 6. A. When        
(     ) 7. A. show        
(     ) 8. A. Isn't      
(     ) 9. A.everything  
(     ) 10.A.important  

B. much         
B. on           
B. countryside  
B. how          
B. lamps        
B. While        
B. showed       
B. Don't        
B. nothing      
B. impossible   

C. rich            
C. over              
C. Guangzhou         
C. what              
C. tables           
C. Before          
C. showing           
C. Won't             
C. something        
C. interesting     

D. poor             
D. around           
D. poor family      
D. which          
D. plants            
D. As soon as       
D. to show        
D. Shan't            
D. anything         
D. satisfied      

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单项选择题

下列船舶中（）在作业所必需的限度内可免受通航制条款的约束。

A.从事捕鱼的船舶

B.从事敷设、维修或起捞海底电缆的船舶

C.从事清除水雷的船舶

D.B、C都是
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