At One Time,Pittsburgh,Pennsylvania,was Known for Its Poor Air Quality

Multiple Choice

At one time,Pittsburgh,Pennsylvania,was known for its poor air quality.Locals said that a man wearing a white shirt when he walked into the city would have a black shirt when he left it.Since that time,the city has greatly reduced its air and water pollution.As a result of cleaner air and water:

A) the standard of living of the citizens of Pittsburgh increased,even though the improvement in the environment was not reflected in its GDP.
B) the value of the GDP increased.
C) the value of the GDP increased in the year that the improvements were made but did not change in ensuing years.
D) the standard of living of the citizens of Pittsburgh did not change.