Competition of Stores

Although the discount stores in Goreville's central shopping district are expected to close within five years as a result of competition from a SpendLess discount department store that just opened, those locations will not stay vacant for long. In the five years since the opening of Colson's, a nondiscount department store, a new store has opened at the location of every store in the shopping district that closed because it could not compete with Colson's.

Which of the following, if true, most seriously weakens the argument?
(A) Many customers of Colson's are expected to do less shopping there than they did before the SpendLess store opened.
(B) Increasingly, the stores that have opened in the central shopping district since Colson's opened have been discount stores.
(C) At present, the central shopping district has as many stores operating in it as it ever had.
(D) Over the course of the next five years, it is expected that Goreville's population will grow at a faster rate than it has for the past several decades.
(E) Manystores in the central shopping district sell types of merchandise that are not available at either SpendLess or Colson's.

Answer is B

I can't understand explanations of OG regarding this question.