In the 1950s, scientists determined that exhaust from cars was a significant
source of air pollution. Since then, the U.S. Environmental Protection Agency
has set standards to reduce the air pollution caused by cars. As a result, auto
and fuel manufacturers have developed new technologies. Which statement
best explains how the market forces of supply and demand guided the
development of these technologies?
A. As car manufacturers developed more fuel-efficient cars, they
began to advertise their environmental benefits to consumers.
B. As consumers purchased more cars that produced less pollution,
car manufacturers made more of these cars and improved their
design to meet the desires of their customers.
C. When a large enough supply of energy-efficient cars became
available, public demand for their use increased.
D. Engineers recognized the health hazards of air pollution and
decided to develop systems that would reduce harmful emissions
from cars.
