Could you please explain to me why C is the correct answer in this question?

Could you please explain to me why C is the correct answer in this question? Thank you.

A particular neuron's resting potential is measured to be constantly fluctuating around -

85mV. Which of the following is the best explanation for this measurement?

A) A number of positively charged sodium ions have moved into the cell via

voltage- gated sodium channels.

B) This neuron's voltage- gated potassium channels are preventing positively

charged potassium from entering the cell.

C) Positively charged potassium ions are exiting the cell at an increased rate due

to hyperactive leaky potassium channels.

D) A number of negatively charged protein molecules have moved along their

concentration gradient into the cell.