Hi,

You make a very good point.

Having only the Na+/K+ pump active, you would expect a higher concentration of intracellular potassium, and thus a more negative value of the resting potential, leaving you with C.

However, the Nernst equation doesn't just rely on the polarization of potassium, but also that of sodium and its permeability. When the permeability of potassium decreases, its contribution to the resting potential decreases and is less significant than that of sodium.

Sodium's resting potential is more positive, and so you would expect the resting potential to shift closer to that of sodium. Thus A seems more plausible.

I would also note that this situation seems similar to the start of an action potential, where the membrane depolarizes.

That being said, it's a tricky question and I think just eliminating to A and C is a good outcome.

Please let me know if this is unclear.