In the Sinoatrial (SA) Node, Phase 4 Depolarization (Pacemaker Potential) $\mathrm{K}^{+}$

In the sinoatrial (SA) node, phase 4 depolarization (pacemaker potential) is attributable to

A) an increase in $\mathrm{K}^{+}$ conductance
B) an increase in $\mathrm{Na}^{+}$ conductance
C) a decrease in $\mathrm{Cl}^{-}$ conductance
D) a decrease in $\mathrm{Ca}^{2+}$ conductance
E) simultaneous increases in $\mathrm{K}^{+}$ and $\mathrm{Cl}^{-}$ conductances