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

完形填空
完型填空。
     Once a rich woman invited Martin Brown, a famous singer, to sing for her fiends. But she   1   him to
have dinner with them. She told him to eat   2   the servants.
     After the meal Martin stood up and said to the servant, "Now, my good friends, I   3   for you." He sang
several songs and the servants were quite   4  .
     Then the rich woman asked   5   to come to the sitting-room. "We are waiting for your songs.   6   you
ready?" the woman asked.
     "I am sorry," Martin said. "I have sung   7  . I usually   8   once in one evening, and I can't sing   9  ".
     And with a polite " 10 ", he left the rich woman's house.
( )1. A. doesn't invite
( )2. A. with          
( )3. A. sang          
( )4. A. sad           
( )5. A. the servant   
( )6. A. Were          
( )7. A. ever          
( )8. A. sings         
( )9. A. one           
( )10. A. Good night   		B. don't invite  
B. for           
B. will sing     
B. bored         
B. the friend    
B. Is            
B. already       
B. will sing     
B. two           
B. Good morning     		C. didn't invite 
C. at            
C. sing          
C. exciting      
C. the woman     
C. Are           
C. never         
C. sing          
C. once          
C. Good afternoon     		D. haven't invite    
D. in                
D. was singing       
D. happy             
D. the singer                   
D. Be                
D. yet               
D. sang              
D. twice             
D. Good day          
查看答案
单项选择题

茎干病害的潜育期一般在（）以上。

A.3年

B.3个月

C.半个月
查看答案