Help! a question about sentence structure

jackfengUID: 2181509

Could any NR give me the right answer regarding the following sentence:

(Though there) has been controversy (as to) the relative nutritional merits of white bread and bread (made) from whole wheat-flour (of) much longer extraction, which is dark in color.  

I guess A is the answer, but I don't know why and how to modify this sentence.
what does "as to" mean here? and how to translate the entire sentence?

thank u in advance! ---from a greenhand of TOEFL

逆风飞羊UID: 182440

我认为是A 问题在于这句话没有完整的结构.把though去掉至少就有主语和谓语了.
as to~~~偶也不知道  @_@!!

uspresidentUID: 2123602

选a，不然就没有主句了。