Which of the follow statements about action potentials are true?

I) A neuron’s resting potential is -55 mV.

II) An all-or-nothing response means once the threshold is reached, the action potential will fire.

III) The refractory period means there is a time where the neuron can’t fire.

• A. I & II only.
• B. I & III only.
• C. II & III only.
• D. I, II, & III.