lsat-15-2-10

The government of Penglai, an isolated island, proposed eliminating outdoor adverting except for small signs of standard shape that identify places of business. Some island merchants protested that the law would reduce the overall volume of business in Penglai, pointing to a report done by the government indicating that in every industry the Penglai businesses that used outdoor advertising had a larger market share than those that did not.

Which one of the following describes an error of reasoning in the merchants’ argument?

(A) presupposing that there are no good reasons for restricting the use of outdoor advertising in Penglai

(B) assuming without giving justification that the outdoor advertising increased market share by some means other than by diverting trader from competing businesses

(C) ignoring the question of whether the government’s survey of the island could be objective

(D) failing to establish whether the market-share advantage enjoyed by businesses employing outdoor advertising was precisely proportionate to the amount of advertising（B）

(E) disregarding the possibility that the government’s proposed restrictions are unconstitutional

Why the answer is B ?