Derived demand refers to the demand for a good or service that is not valued for its own sake but is derived from the demand for another related good or service. In this context, the option that best illustrates derived demand is:
b an increase in the number of new single-family homes results from a spurt in the growth of the local population.
The explanation for this is that as the population grows, more housing is needed to accommodate the increased number of residents. Therefore, the demand for single-family homes is driven by the underlying demand for housing created by the growing population. In contrast, option a highlights a change in retail stores and demand for goods but does not directly illustrate the concept of derived demand as clearly as option b does.