Which action(s) could contribute to the positive inotropic effect of digoxin on cardiac myocytes?
I. Decrease transport of Ca2+ to the extracellular environment.
II. Increase availability of intracellular Ca2+ to bind to troponin.
III. Increase overall Ca2+ stores in the sarcoplasmic reticulum.
A.II only
B.III only
C.I and II only
D.I, II, and III
