How Can Organisms Perceive Different Intensities of a Stimulus

How can organisms perceive different intensities of a stimulus?

A) by an increase in intensity and frequency of action potentials generated as well as an increase in the number of cells generating action potentials
B) by an increase in the frequency of action potentials generated by an afferent neuron
C) by an increase in intensity of the action potentials generated by an afferent neuron
D) by an increase in the frequency of action potentials generated as well the numbers of afferent neurons generating action potentials, but not the intensity of action potentials