B.
What are vegetative organs?

External plant structures such as leaves, stems, roots, flowers, fruits, and seeds are known as plant organs. Vegetative parts  include roots, stems, shoot buds, and leaves; they are not directly involved in sexual reproduction.

the answer that best describes the relative refractory period in the neuron is the resting membrane potential is restored, but concentrations of sodium and potassium are not restored to their original state.

the refractory period is the time during which another stimulus given to the neuron will not lead to a second potential. thus, because na+ channels are inactivated during this time, additional depolarizing stimuli do not lead to new action potentials.  

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that is wrong, its not thymus.