It is often observed that, over the same period of time and for the same good, marginal utility declines rapidly for some consumers and very little for others. This observation illustrates:

a. that economic theory is of little value in explaining consumer behavior.
b. that consumers are not identical.
c. tastes and preferences should not be included in any discussion of consumer choice.
d. tastes and preferences among consumers are quite similar.
e. that if consumers weren't identical, economic theory would not be able to provide insight into consumer behavior.

b