After drinking several cups of strong coffee, a person develops "coffee nerves" or "jitters." This probably is due to the ability of caffeine to ________

a. block adenosine receptor sites
b. cause neurotransmitters to leak out of the synaptic vesicles and be destroyed by enzymes
c. cause an increase in the release of excitatory neurotransmitters
d. inhibit enzymes which break down excitatory neurotransmitters

Answer: a