It could be argued that the era of modern medicine began in earnest wi

Dear sumanainampudi,

I'm happy to respond.

My friend, when you post a SC question, please always underline the prompt correctly. It's also in good form to write in the answer choice letters. The habit of excellence extends to the details. How you do anything is how you do everything.

It's true that, grammatically, in the structure "X of Y, which" the word "which" could refer to either X or Y, depending on context.

Of course, the GMAT SC is NOT just a test of grammar--instead, grammar & logic & rhetoric are all equally important. Here, the problem with "which" is logical as much as grammatical, although the book's OE didn't go into this.

Even if "which" refers to "vaccine," the "vaccine for rabies," by itself, did not lead to "the eradication of polio, smallpox, and eventually malaria." Instead, the ideas suggested by the rabies vaccine, that general method, lead to the eradication of the other diseases. If we could construe the word "which" as targeting "development," then it would logically make sense, but at that point, we are expecting the modifier to leapfrog over two other nouns. The target of "which" is quite muddled and unclear.

Inserting the word "event" solves all these problems. That's why (C) is the best answer.

There are often many things to say about why a wrong answer is wrong in a well-designed question. Sometimes, simple space constraints limit the length of the explanations. Don't automatically assume that the explanation printed in the book is all there is to say on the subject. The OEs in the GMAT OG are particularly disappointing in this regard.

Does all this make sense?
Mike