Taking into account air quality legislation prior to 1970, why is the 1970 Clean Air Act considered the beginning of the modern era in clean air legislation?

At least three references 

QUESTION 1

Write an essay consisting of at least 550 words addressing all of the following topics (a through d):

a. Taking into account air quality legislation prior to 1970, why is the 1970 Clean Air Act considered the beginning of the modern era in clean air legislation? 

b. List the parameters that are on the NAAQS. 

c. Explain how the U.S. President and/or U.S. Congress influence the U.S. EPA. 

d. Explain the pros and cons of MTBE