Some part of the given sentence is underlined.Four choices for rephrasing the underlined part follow each sentence.Please tell me which option is grammatically correct and effective.

Jamieson's proposal wa rejected for several reasons,the chief among which was cost.

(a) the chief among which was cost
(b) the chief of which was cost
(c) among which the chief was its cost.
(d) the chief reason of which was its cost.

Please let me know which option is correct and why are the others incorrect.Any help is appreciated.
None are clearly wrong. If this is some sort of test, it's not a very good one.
Yeah,this is from a test. And a very reputed test all over the world. So the question is a standard one.
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To me, (b) is the answer.
it is most probably the third choice "c"