The answer is letter B.
Motor neurons tend to function less as age sets-in in a particular individual. Reaction time is the ability to respond quickly to stimulus presented in a given situation. An example of this is the gun start that is commonly used in athletic competitions where a person reacts quickly to the signal and performs the activity. As we age, our sensory systems deteriorate and as a result some of the skills we have when we were younger are not as effective as it was when we turned into mature adults.