HomeFront Construction Company built large, single-family homes for 25 years. Then there was a shift toward more demand for small luxury condominiums, and HomeFront changed its focus. The change in demand could be explained by: a. the increasing number of senior citizens who are "empty-nesters."
b. the fact that consumers in urban areas generally have higher incomes.
c. the increasing number of 45-64 year olds whose children are grown.
d. All of these explanations could be relevant.