Question

cancer causing substances. at least 43 of these present in tobacco.
carcinogens
stimulant
nds - e-cigarette
leukoplakia
nicotine

Explanation:

Carcinogens are defined as substances that cause cancer, and it is established that at least 43 carcinogens are present in tobacco. Nicotine is an addictive stimulant, not a direct cancer-causing substance in this context. Stimulant is a broad category of substances that increase activity, not specific to cancer-causing agents. NDS - E-Cigarette refers to a product, not a cancer-causing substance. Leukoplakia is a pre-cancerous condition, not a substance.

Answer:

A. Carcinogens