Sentence Correction

233. Darwin was not the first to advance a theory of evolution; his tremendous originality lay in the fact that he proposed the idea of natural selection as the means by which evolution worked.
(A) lay in the fact that he proposed the idea
(B) lay in the fact of his proposing the idea
(C) laid in the fact of his proposing the idea
(D) laid in his proposal
(E) lay in his proposal


Why lay , why not laid......