The correct answer is on.
Alcohol acts on the brain by inhibiting the activity of the neurotransmitter GABA. This causes a decrease in inhibition, which can lead to a number of effects, including impaired judgment, coordination, and decision-making. Alcohol can also increase the activity of the neurotransmitter dopamine, which can lead to feelings of pleasure and euphoria.
The other options are incorrect because they do not accurately describe how alcohol acts on the brain. Option A, “by,” is incorrect because it does not specify how alcohol acts on the brain. Option B, “by,” is incorrect because it does not specify which part of the brain alcohol acts on. Option C, “on,” is incorrect because it does not specify how alcohol affects the brain. Option D, “with,” is incorrect because it does not specify how alcohol interacts with the brain.