The relative refractory phase in an action potential refers to:a. When the membrane is depolarized due to the opening of voltage-gated K+ channelsb. When the membrane is depolarized due to the opening of voltage-gated Na+ channelsc. When the membrane is hyperpolarized due to the opening of voltage-gated K+ channelsd. When the membrane is hyperpolarized due to the opening of voltage-gated Na+ channelse. When the membrane is at its resting potential