Prolonged Use of Amphetamines Has Been Linked to an Increase

Prolonged use of amphetamines has been linked to an increase in violent behavior, but it is not easy to interpret this link because

A) there are many different definitions of violence.
B) people are usually not willing to admit that they have taken amphetamines.
C) the violence could be due to the drug user's lifestyle, not the drug itself.
D) very few people actually engage in prolonged use of amphetamines.