_云南成考网

Scientists have discovered that what prevents people from concentrating is_____.

• A、any kind of noise
  

• B、great changes in level of  noise
  

• C、background noise
  

• D、various background music
  
  

This selection was probably written to____．

• A、show how lazy eats are
  

• B、talk about the habits of eats
  

• C、tell about famous people and their habits
  

• D、persuade people to take naps

52.__________