大全 191

191. 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,

As to answerB, what is wrong with it? 是因为它中间的插入语太长，使a derivative 和of the Madagascar periwinkle 相隔太远么？

thanks

谢谢stoneren，回答了我很多问题

请问这句话想要表达的是 the derivative of the Madagascar periwinkle “has proved useful in decreasing mortality among young ..., ” 是这样么?

注意主句的结构：主语：A derivative，谓语：is cultivated；事实上是periwinkle被种植而不是derivative；而且derivative后一个非限定性定从也错了

你区分是不是非限制性定语丛句是根据derivative后的逗号么？