Several years ago the diet industry introduced a variety of appetite suppressants, but some of these drugs caused
stomach disorders severe enough to have them banned by the Food and Drug Administration.
(A) stomach disorders severe enough to have them —
"them" is unclear, are we talking about the stomach disorders or the drugs ?(B) stomach disorders that were severe enough so they were —
idem for "they"(C) stomach disorders of such severity so as to be —
it implies that the stomach disorders were banned, it is illogical(D) such severe stomach disorders that they were —
THE DRUGS CAUSED (such severe stomach disorders) THAT THEY, here it is logical that the drugs are the antecedent of "they", actually stomach disorders is part of the modifier of "caused"(E) such severe stomach disorders as to be —
Idiom is "SO AS TO BE"Hope that it helps,