The correct answer is D. Polycyclic hydrocarbons.
Polycyclic
hydrocarbons are a group of chemicals that are formed when organic matter is burned. They are found in the exhaust of gasoline-powered vehicles, as well as in cigarette smoke and other sources of air pollution.Polycyclic hydrocarbons are known to cause cancer in animals, and there is strong evidence that they also cause cancer in humans. They are thought to cause cancer by damaging DNA, which can lead to the uncontrolled growth of cells.
Oxides of nitrogen are also found in automobile exhaust, but they are not known to cause cancer. Carbon monoxide is another gas found in automobile exhaust, and it can be fatal if inhaled in high concentrations. However, it is not known to cause cancer. Lead is a metal that was once used in gasoline, but it is no longer used in the United States. Lead can cause brain damage and other health problems, but it is not known to cause cancer.
In conclusion, the correct answer is D. Polycyclic hydrocarbons.