IMO E
(A) An extract of the plant Decalepis hamiltonii, which has proved helpful in protecting brain cells from damaging effects of alcohol, ------ An Extract cannot be grown. Meaning Error
(B) An extract, which has proved helpful in protecting brain cells from damaging effects of alcohol, comes from the plant Decalepis hamiltonii,---- Same Error as A. A Plant is grown not an extract.
(C) A Decalepis hamiltonii extract, which has proved helpful in protecting brain cells from damaging effects of alcohol,---- Same error as A and B.
(D) The Decalepis hamiltonii plant has an extract, which has proved helpful in protecting brain cells from damaging effects of alcohol,----- If you eliminate the fluff, the sentence says "has an extract is grown in India" Sounds like a run on
(E) The Decalepis hamiltonii plant, an extract of which has proved helpful in protecting brain cells from damaging effects of alcohol, ----Correct.At least that's what I think