A researcher reports that a drug indirectly stimulates a reward center in the brain rather than directly stimulating it. The drug the researcher is studying could be any of the following drugs EXCEPT: alcohol. opium. marijuana. cocaine.

Cocaine

Explanation:

All addictive drug directly or indirectly activate or stimulate the reward center. Alcohol, opium and marijuana indirectly stimulates the reward center through the peripheral nerves. In the case of cocaine, this drug directly activates or stimulates the reward center instead of through peripheral nerves.

Normally, during neural communication process, dopamine is released into the synapses by a neuron, where it is able to bind to dopamine receptors in other neuron and further recycled through the dopamine transporter  into the transmitting neuron. In the presence of cocaine, the dopamine transporter is blocked resulting in dopamine build up hence stimulating the reward system.

the first question's answer is a.

answer; all over the above; //everybody