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The graph depicts the potential voltage changes across a cell membrane; these changes (depolarization, repolarization, hyperpolarization, and resting potential) are collectively known as the action potential.  The action potential occurs due to changes in the membrane permeability to Na⁺ and K⁺ ions.  The membrane potential of an excitable cell (eg, nerve and muscle) cycles through the following stages:

1. Resting potential (Choice A):  Usually equal to -70 mV.  It is maintained by high resting membrane permeability to K⁺ and low permeability to Na⁺.  K⁺ efflux occurs via non-gated K⁺ channels (leak channels).  While at the resting potential, the inner side of the membrane is negatively charged with respect to the outer surface of the membrane.
2. Depolarization:  Occurs due to opening of voltage-gated Na⁺ channels with rapid influx of Na⁺ into the cell.  The large influx of Na⁺ leads to an increased positive charge inside the membrane known as depolarization (Choice B).  Overshoot refers to the maximal value of the action potential during which the membrane potential obtains a positive value (approximately +35 mV) (Choice C).
3. Repolarization (Choice D):  Results from closure of Na⁺ channels and simultaneous opening of K⁺ channels.  This causes a sharp decrease in the membrane permeability to Na⁺ and a significant increase in K⁺ permeance that exceeds that of the resting membrane.  K⁺ efflux is responsible for returning the membrane potential back to the resting potential.
4. Hyperpolarization (Choice E):  Occurs because the voltage-gated K⁺ channels remain open for a short time after repolarization is completed.  The membrane potential thus becomes more negative than the normal resting potential and approaches the K⁺ equilibrium potential of -85 mV.  When the voltage-gated K⁺ channels close, the membrane potential returns to the resting value maintained by the non-gated K⁺ channels.

Educational objective:
The action potential results from changes in the membrane permeability to K⁺ and Na⁺ ions.  Depolarization results from massive influx of Na⁺ through voltage-gated Na⁺ channels.  Repolarization occurs due to closure of voltage-gated Na⁺ channels and opening of voltage-gated K⁺ channels.  K⁺ ion permeance is highest during the repolarization phase of the action potential.