@peas please go through this:

Can Which" modify the immediately preceding noun only ?
OR
Is it that if i have a sentence of the form "A of B,which".. The "which" may refer to either A or B depending on the context ?
from what we've seen, the gmat is actually pretty consistent on this issue.

Ron's Comments:

what we've seen, so far, is:

the gmat tends to write sentences in which "which" stands for the ELIGIBLE noun that's closest to the comma.
by "eligible", i mean that the noun has to AGREE IN TERMS OF SINGULAR/PLURAL with the FOLLOWING VERB.

here's an example:

the box of nails, which is on the counter, is to be used on this project.

in this case, "which" CANNOT refer to "nails", since the verb "is" is singular. therefore, the nearest eligible noun is "box (of nails)". so, "which" unambiguously stands for that.

in our observation, the gmat has been VERY good about this.
whenever i've seen a "which" that refers to "X of Y" rather than just Y, it has ALWAYS been the case that X was singular and Y was plural (or X was plural and Y was singular), and the verb had a form that matched X and didn't match Y.

hope that helps.

Ankur,

I explained the same thing in my first post.
I wrote that 'grammatically there is nothing wrong in E'.

Which can refer to effectiveness also. [because given verb is for singular subject]

Ron also is saying the same thing,

But he explained that its valid for 'OF' .Will it be valid for 'In' also?

yes.
valid for any preposition.

Thanks dear..when are you planning to take GMAT

ankurmit wrote:Thanks dear..when are you planning to take GMAT

not decided yet.
will try to finish by sep. end.