20. Cathy, along with his teacher, (   ) to Guangzhou on business. 

• A、have gone
  
  

• B、has gone
  
  

• C、are going
  
  

• D、have been gone
  
  

40. The main idea of this passage is (   ).

• A、warfare is a "law of nature"
  
  

• B、warfare is not a "law of nature"
  
  

• C、warfare does not control human population
  
  

• D、none of the lowlier animals, except ants, practice warfare upon their own species
  
  

52 .(    ).