Which of the following statements about voltage-gated potassium channels are CORRECT?
a) Voltage-gated potassium channels sense transmembrane voltage potential to control the opening and closing of the channel.
b) Voltage-gated potassium channels contain only four transmembrane helices.
c) Peptide carbonyl oxygens position water molecules to correctly hydrate the ions and allow for their passage.
d) Voltage-gated potassium channels can allow potassium and smaller ions, such as sodium, pass but not allow larger ions such as rubidium.