answer: #Person1# thinks the biggest environmental problem is air pollution majorly caused by cars. #Person1# and #Person2# agree that they need international cooperation.
documents: #Person1#: I think the biggest environment problem in my country is air pollution. 
  #Person2#: Yes, I agree. The air here is much more polluted than in my country. Of course, my country is more agricultural and has much less industry. 
  #Person1#: We have reduced emission of air pollutants in recent years,but cars are still a major source of them. Factories have become cleaner as stricter environment pollution law have been introduced. 
  #Person2#: The problem is now on a truly global scale. I don't believe that any single country can do anything about it. 
  #Person1#: I think you're right. There needs to be an international response to this problem?