Notice the trend in the graph of vehicular lead emissions in the United States from 1970 to 2011. Which of the following
explanations best support the trend shown?
A. By 1990, all new model cars were equipped with internal fabric filters that
effectively filtered car exhaust and reduced lead emissions.
B. Beginning in 1975, The Clean Air Act required new cars to have catalytic
converters, which effectively converted the lead found in gasoline to water
vapor.
C. New air-scrubber technologies were introduced in the late 1970s that
effectively removed lead in the air and converted it into water vapor.
D. Unleaded gasoline was first introduced in 1974, and amendments to the Clean
Air Act required cars with the model year 1975 or later to use only unleaded
gasoline.