Parasympathetic Stimulation of the Heart Generally Leads to a Decrease $\beta$

Parasympathetic stimulation of the heart generally leads to a decrease in heart rate because acetylcholine

A) increases intracellular cAMP levels and opens calcium channels.
B) opens potassium channels allowing potassium ion efflux.
C) binds and blocks $\beta$ receptors on the cell membrane.
D) inhibits voltage-gated sodium channels in the membrane.