The correct answer is:
b. carbon monoxide and tar
Nicotine, carbon monoxide, and tar are all harmful chemicals found in cigarettes. Carbon monoxide is a poisonous gas that interferes with the body's ability to transport oxygen, and tar is a sticky substance that accumulates in the lungs and can cause respiratory issues. Nicotine is a highly addictive substance that is responsible for the addictive nature of cigarettes, while carbon monoxide and tar are also dangerous chemicals that contribute to the harmful effects of smoking. Stimulants and tobacco are not the correct options as they do not accurately represent the harmful chemicals found in cigarettes.