Voltage-Sensitive K⁺ Channels Are 1,000 Times More Permeable to K⁺

Voltage-sensitive K⁺ channels are 1,000 times more permeable to K⁺ than to Na⁺ because

A) K⁺ ions are smaller than Na⁺ ions.
B) K⁺ ions have a lower charge density than Na⁺ ions.
C) a selectivity filter removes the water molecules from K⁺ ions but not from Na⁺ ions.
D) K⁺ ions are more concentrated inside the cell than outside the cell.