The imposition of quotas limiting imported steel will not help the big American steel mills. In fact, the quotas will help “mini-mills” flourish in the United States. Those small domestic mills will take more business from the big American steel mills than would have been taken by the foreign steel mills in the absence of quotas.
Which of the following, if true, would cast the most serious doubt on the claim made in the last sentence above?
(A) Quality rather than price is a major factor in determining the type of steel to be used for a particular application.
(B) Foreign steel mills have long produced grades of steel comparable in quality to the steel produced by the big American mills.
(C) American quotas on imported goods have often induced other countries to impose similar quotas on American goods.
(D) Domestic “mini-mills” consistently produce better grades of steel than do the big American mills.
(E) Domestic “mini-mills” produce low-volume, specialized types of steels that are not produced by the big American steel mills.

Please lemme know why B is incorrect.. I think B implies that foreign steel mills quality of steel comparable to big american mills, so foreign mills can take away the big american mills business, hence cast doubt or weakens the claim made in the last statement of the stiluli.