问题 选择题

如图所示实验,说明了二氧化碳(  )

A.不能燃烧,也不能支持燃烧;密度比空气的大

B.二氧化碳的密度比空气大

C.二氧化碳可与蜡烛发生反应

D.二氧化碳通常为无色无味的气体

答案

将二氧化碳气体慢慢倒入燃着两只蜡烛的烧杯中,观察到的现象是下层的蜡烛火焰先熄灭,上层的蜡烛火焰后熄灭,这是因为CO2密度比空气大,不能燃烧、不能支持燃烧的缘故,根据二氧化碳的上述性质,二氧化碳可以用于灭火.

答案:A.

选择题
完形填空
完形填空。

      Peter and Paul had got permission from their parents to camp in a field close to their
farm.But,being adventurous boys,they knew it would be more   1   to camp in the woods
that lay beyond the river.Excitedly,the boys   2   with their tent and food.
     Carrying their heavy   3  ,the two brothers walked along the riverbank,hardly noticing
the distance or the sun beating down.They were eager to reach their   4   before lunchtime.
As they entered the cool,shadowy woods,they began to search for a suitable camping spot.
Peter wanted to   5  close to the river at the edge of the woods,  6   Paul,who was older,
insisted that they camp further away.  7  ,Peter followed his brother deeper into the   8  .
"This really is a wonderful setting!" said Paul in excitement.They   9   their tent,and settled
down to eat the sandwiches they had made,then decided to find their way   10   to the river
to catch some fish.
     "Are you sure that this is the right   11  ?" whispered Peter shakily."I'm sure we passed that
hollow tree just a while ago." Paul walked   12   silently."Look,there it is again.We're lost,aren't
we?" complained Peter.Paul had to admit that he didn't know where they were.  13  ,they were
a long distance from where they were   14   to be.They were not even   15   of where they had
set up their camp.They set in   16   for a few minutes until Peter had a bright idea."Why don't we
look for clues(线索)the way that trackers   17   in the movies?We weren't careful about how we
 walked,so I'm sure we would have left   18   some broken tree branches and leaves."
     Carefully,the boys   19   the marks that they had left,until finally they found their campsite.
Hurriedly,they packed their belongings and set off   20   the direction of the river. 
      What would their parents think of their adventure?

( )1.A.surprising  
( )2.A.went round  
( )3.A.load        
( )4.A.grassland  
( )5.A.live        
( )6.A.but        
( )7.A.Unconsciously
( )8.A.woods      
( )9.A.put off    
( )10.A.forward    
( )11.A.place      
( )12.A.alone      
( )13.A.After all  
( )14.A.discovered
( )15.A.afraid    
( )16.A.enjoyment  
( )17.A.appear    
( )18.A.behind    
( )19.A.fetched    
( )20.A.for        
B.exciting    
B.went back    
B.tent        
B.destination  
B.lie          
B.and          
B.Unfortunately
B.farm        
B.put on      
B.near        
B.mark        
B.about        
B.At last      
B.encouraged  
B.sure        
B.satisfaction
B.do          
B.out          
B.watched      
B.to          
C.annoying    
C.went away    
C.food        
C.field        
C.wait        
C.or          
C.Unwillingly  
C.setting      
C.put down    
C.back        
C.way          
C.in          
C.Above all    
C.persuaded    
C.informed    
C.disappointment
C.work        
C.aside        
C.followed    
C.at          
D.frightening    
D.went through  
D.storage        
D.river          
D.stay          
D.so            
D.Uninterestingly
D.camp          
D.put up        
D.further        
D.time          
D.on            
D.At first      
D.supposed      
D.reminded      
D.imagination    
D.behave        
D.around        
D.collected      
D.in