Sentence Correction

33. A substance derived from the Madagascar periwinkle, which has proved useful in decreasing mortality among young leukemia patients, is cultivated in China as part of a program to integrate traditional herbal medicine into a contemporary system of health care.
(A) A substance derived from the Madagascar periwinkle, which has proved useful in decreasing mortality among young leukemia patients,
(B) A derivative, which has proved useful in decreasing mortality among young leukemia patients, of the Madagascar periwinkle,
(C) A Madagascar periwinkle derivative, which has proved useful in decreasing mortality among young leukemia patients,
(D) The Madagascar periwinkle has a derivative which has proved useful in decreasing mortality among young leukemia patients, that
(E) The Madagascar periwinkle, a derivative of which has proved useful in decreasing mortality among young leukemia patients,

E isn't " of which" unidiomatic?

IMO e

Rest all changes the meaning

(A) A substance derived from the Madagascar periwinkle, which has proved useful in decreasing mortality among young leukemia patients,

Improper antecedent - which can refer to either 'substance' or 'Madagascar periwinkle'

(B) A derivative, which has proved useful in decreasing mortality among young leukemia patients, of the Madagascar periwinkle,

Change in meaning - young leukemia patients of Madagascar periwinkle

(C) A Madagascar periwinkle derivative, which has proved useful in decreasing mortality among young leukemia patients,

"A madagascar periwinkle derivative" - change in subject.

(D) The Madagascar periwinkle has a derivative which has proved useful in decreasing mortality among young leukemia patients, that

Improper usage of That

(E) The Madagascar periwinkle, a derivative of which has proved useful in decreasing mortality among young leukemia patients,

Only option left - has to be correct

E should be the answer

Derivative cannot be cultivated...

Madagascar periwinkle has to be cultivated.. this is clear in E only