When a motor neuron and the skeletal muscle cell it innervates are at rest: ?

Particularly the skeletal muscles at rest gain most of their energy from the aerobic respiration of fatty acids. Hence fatty acids provide the majority of the energy for muscle metabolism when a person is exercising at 25% of VO2max. However, the motor neuron is at rest when a neuron is not receiving any input there will be a potential difference. Thus, the potential difference measured when the neuron is inactive and it is caled the resting membrane potential. 

answer: b

coz red blood cells marrow and circulates the body for 120 days.