The endogenous opioid system is involved in the reinforcing effects of
A) alcohol.
B) cocaine.
C) marijuana.
D) methamphetamine.
Question 2
Researchers who have studied the risk for alcohol dependence among family members have found that about _____ percent of the variance in liability may be due to genetic influence.
A) 10-20
B) 20-30
C) 30-40
D) 50-60