Amotor unit is defined as:
a) all the muscle cells in a whole muscle
b) all the muscle cells innervated by a single motor neurorn
c) all the neurons that nnervate a single whole muscle
d) the total force at which a whole muscle can generate

The answer is B: All the muscle cells innervated by a single motor neurorn.

Explanation:

It is called a motor unit, all muscle fibers that are innervated by a motor neuron cell. A motor neuron cell can establish contact with up to 150 muscle fibrils, which when activated causes their simultaneous contraction, therefore, all the muscle fibers of a motor unit contract and relax at the same time.