Answer:
The most correct option is;
B. An increase in air emission standard which began in 1970 that regulated corporate average fuel economy standards
Step-by-step explanation:
In 1966, due to the introduction of the control of pollution from motor vehicle emission standard which required air pumps with a higher efficiency and the 1970 requirements set to ensure automobile manufacturers attain the smog forming combustion control standards evidence has shown modern automobiles emit much less smog forming hydrocarbon and VOCs than they did in the 50s' or 60s'
The Corporate Average Fuel Economy (CAFE) standards came into effect in 1975 improving fuel efficiencies by up to 14%.