The prices for all kinds of fish sold in Eastville's downtown Old Market are much lower than the prices charged at uptown seafood stores. Old Market vendors buy fish of similar quality from the same wholesalers and at the same prices as uptown vendors do. Therefore, since Old Market fish vendors' businesses are as profitable as those uptown, the volume of the Old Market vendors' daily fish sales must, on average, be higher. Which of the following, if true, most strengthens the argument given?
A. People who buy fish at Old Market stores generally have lower incomes than do those who buy fish from uptown seafood stores.
B. Some varieties of fish that are not available at Old Market stores can be found occasionally at uptown seafood stores.
C. Vendors at the old Market save on energy costs by keeping fish on ice instead of in refrigerated cases.
D. Many of the people who live in uptown Eastville prefer to buy fish from the neighborhood stores.
E. Fish vendors at the Old Market do not, on average, have lower overhead costs than uptown vendors do.