Answer: C. ATP supplies energy for sodium–potassium pumping, which establishes and maintains ion concentration gradients. With less ATP, pump activity decreases; over time, the gradients weaken and the resting potential becomes less negative.

A: predicts weaker gradients but reverses their effect on the resting potential. B: assumes the pump becomes more active despite reduced ATP availability. D: treats the pump as dissipating, rather than establishing and maintaining, concentration gradients.

Remember: ATP-driven pumping maintains the ion gradients that support the resting potential.