Final answer:
The reinforcing effects of alcohol may be due to increased activation of GABAA receptors, which leads to decreased excitability of neurons and a calming effect on the brain. Correct option is 5.
Step-by-step explanation:
The reinforcing effects of alcohol may be due to increased activation of GABAA receptors. Alcohol enhances the inhibitory effect of GABA receptors, leading to decreased excitability of neurons and a calming effect on the brain. This is why alcohol consumption can result in feelings of relaxation and sedation.