21. Reports say that the walkers are mostly from（）

• A、we divide a 30-minute walk into 3 parts
  
  

• B、our in activeness
  
  

• C、we may like to try a longer one
  
  

• D、big cities in America
  
  

• E、a daily 30-minute quick walk
  
  

• F、a face-to-face talk
  
  

A. It has always been a great barrier to people traveling south.

B. This oil is shipped to many parts of the world.

C. Each region has its special geography and history.

D. Asia is much larger than Europe.

E. All these people have left their influence there.

F. About 40 million people live there today.

17.Paragraph 2:

• A、The key to walking is getting started.
  
  

• B、Walking is the first step to making changes.
  
  

• C、The advantage of walking is its simplicity.
  
  

• D、Walking is a great way for health improvement.
  
  

• E、More Americans take up walking than before.
  
  

• F、Modern lifestyle affects our health negatively.