The belief that tobacco is a "gateway drug" is consistent with
a. most of the available evidence.
b. the idea that an increase in income causes a decrease in the demand for tobacco and an increase in the demand for marijuana.
c. the idea that tobacco and marijuana are substitutes.
d. the idea that lower cigarette prices are associated with less use of marijuana.

C

Explanation:

There was a study that revealed that tobacco products could react as a gateway drug opening the door to the use of the illicit drug. Use of drug and tobacco raise the risk of later use of illicit drugs like marijuana and cocaine. In a recent survey, it is found that 90% of users of cocaine among adults between the ages of 18 to 35 used cigarettes before used cocaine. Researchers was in suspension  that nicotine exposure may be  increased vulnerability to cocaine. So no one found a biological mechanism. The findings suggest that lowering smoking rates in young people might help reduce cocaine abuse.

where is the passage

answer; knowledge,reason,and judgement;