Final answer:
Caffeine influences the activity of the neurotransmitters norepinephrine and serotonin.
Step-by-step explanation:
The correct answer is a) Norepinephrine and serotonin. Caffeine influences the activity of these two neurotransmitters. It acts as an antagonist to the adenosine receptor, which suppresses the release of norepinephrine at synapses. By blocking adenosine's activity, caffeine indirectly increases adrenergic activity, leading to increased levels of norepinephrine and serotonin in the brain.