Question

drugs that affect the brain by increasing ________ activity are the most commonly misused ones. insulin melatonin dopamine adrenaline

Explanation:

Insulin regulates blood - sugar and is not related to brain activity in this context. Melatonin is related to sleep - wake cycles. Adrenaline is involved in the body's stress response. Dopamine is a neurotransmitter in the brain, and drugs that increase dopamine activity are highly addictive and commonly misused as they produce feelings of pleasure and reward.

Answer:

C. dopamine