问题 选择题

在观察洋葱内表皮细胞时,最容易看到的细胞结构是(  )

A.细胞膜和细胞质

B.细胞壁和细胞质

C.细胞壁和细胞核

D.细胞壁和细胞膜

答案

洋葱表皮细胞的结构包括细胞壁、细胞膜、细胞质、细胞核和液泡,其中细胞膜是紧贴着细胞壁的一层透明薄膜,在低倍显微镜下是看不见的.

A、细胞膜是紧贴着细胞壁的一层透明薄膜,在低倍显微镜下是看不见的.故此选项不符合题意;

B、洋葱表皮细胞的细胞壁、细胞质,在低倍的显微镜下可以看到,但不是最容易看到的细胞结构,故此选项不符合题意;

C、洋葱表皮细胞的细胞壁、细胞核,在低倍的显微镜下是最容易看到的细胞结构,细胞核染色最深,故此选项符合题意.

D.细胞膜在低倍显微镜下是看不见的.故此选项不符合题意;

故选:C.

完形填空
完形填空。
     I work as a postal letter carrier in Charlotte. One day several years ago, I drove up to a   1  . Christy, the
young divorcee (离了婚的人)who lived there, was waiting by the roadside. She said that she had a   2   to
tell me.
     About six months   3   it seemed that I had   4   a letter to her which had her street   5   on it but was
addressed to another house with the   6   number on a different street in her neighborhood. She decided to
drop off the letter to the correct house.
     It turned out that the letter had been   7   for Johnson, who happened to be   8  . They talked for a little
while and later on he   9  . Then they started dating (约会) and had been going  10  together ever since.
      I felt sorry for delivering the letter wrong, but I was  11  that I had brought these nice people together.
     A few months later a(n)  12  sign went up in Christy`s yard. and then the wedding  13  were sent out.
Soon the house was sold,the wedding happened,  14   Christy, with her kids, moved into Johnson`s house.
A few months later, I saw a For Sale sign in  15  yard. I feared the  16  might be trouble, so I made up a(n) 
 17  to go to their door and check on them.
     Christy opened the door,smiled broadly, and  18  to her huge stomach "We are having twins!" she said,
 "This house won`t be big enough, so we have to  19  ."
     I suddenly realized that my one  20  letter was now giving two little yet-to-be-born people a shot at life.
Great!
( )1. A. telephone     
( )2. A. story         
( )3. A. after        
( )4. A. sent           
( )5. A. mark          
( )6. A. correct       
( )7. A. provid ed    
( )8. A. simple          
( )9. A. left         
( )10. A. out           
( )11. A. amazed       
( )12. A. At Sale        
( )13. A. arrangements   
( )14. A. but           
( )15. A. her           
( )16. A. friendship    
( )17. A. apology         
( )18. A. pointed      
 ( )19. A. change      
( )20. A. described     
B. mailbox      
B. notice      
B. earlier    
B. written  
B. sign        
B. wrong      
B. prepared   
B. single      
B. invited                  
B. in          
B. pleased    
B. At Sales    
B. preparations 
B. and      
B. his        
B. connection   
B. trouble    
B. attended    
B. settle   
B. misdelivered
C. school        
C. fact          
C. later       
C. delivered      
C. board      
C. same          
C. inferred      
C. lonely        
C. called        
C. away                    
C. surprised      
C. On Sale      
C. invitations    
C. while        
C. my           
C. marriage      
C. excuse        
C. contributed    
C. separate       
C. lost         
D. shop             
D. message          
D. before            
D. given            
D. number           
D. different        
D. intended         
D. free             
D. introduced       
D. off              
D. interested       
D. For Sale         
D. announcements    
D. until            
D. their            
D. wedding          
D. regret            
D. tried            
D. move             
D. delayed        
单项选择题