Suppose you presented a loud tone (high pitch) to a rat and measured his startle response (how high he jumps). Once responding reached asymptote you present a different loud tone (low pitch) of the same intensity and observe that the rat startles at his initial level. This result tells you the following about the response decrements you observed to the first stimulus

A. they cannot be the result of motor fatigue
B. they may be the result of sensory adaptation
C. they cannot be due to a reduction in sensitivity of the muscles to neurotransmitter released by the motor neuron
D. all of the above