Answer:
B) cAMP
Explanation:
Phosphodiesterase is an enzyme that breaks a phosphodiester bond, for example in molecules such as cAMP and cGMP. So, phosphodiestarases are are regulators of signal transduction: regulate the duration of signaling pathway.
Caffeine is central-nervous-system stimulant and the mechanisms of its action usually are: mobilization of intracellular calcium or inhibition of specific phosphodiesterases.
