[quote="Bunuel"]Over the past ten years cultivated sunflowers have become a major commercial crop,
second only to soybeans as a source of vegetable oil.
A. second only to soybeans as a source of vegetable oil
B. second in importance to soybeans only as a source of vegetable oil
C. being second in importance only to soybeans as a source of vegetable oil
D. which, as a source of vegetable oil, is only second to soybeans
E. as a source of vegetable oil only second to soybeans
a phrase, which refers to subject of the main clause and work as adverb is popular in english. the examples are
asked, I do not answer
learning gmat, I understand english more
she has left, tired of you
position of this phrase is flexible, at the begining, in the middle or at the end of the main clause. though this phrase work as an adverb modiying the main verb, it refer to the subject , meaning the action or attributes belong to the subject.
choice A in our problem is this pattern.