大全33，一个知识点的的疑问，有关 of which

1.        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）

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

选项E的of which修饰的是什么。我觉得 a derivative是 The Madagascar periwinkle的同位语。但是这样的话 of which是指代什么呢？难道是说 The Madagascar periwinkle 是 The Madagascar periwinkle自己的 derivative？

不弄明白睡不着啊

我刚发了这个题，也是很不明白，觉得E不对。那Madagascar periwinkle在E 不是主语么？若是主语，则这个选项的意思就和原文不一样了。原文在说一种Madagascar periwinkle的萃取物，而不是他本身。查了字典，这个是一种植物。

a derivative of which has proved useful in decreasing mortality among young leukemia patients怎么做同位语？derivative和Madagascar periwinkle根本就不是同位语