Since research is uncountable,you should associate it with amount.Hence since it signifies an uncountable quantity,it will be singular as given in B.Also the research is being carried out into the cause of accoustic neuromas.Hence research and the phrase into the cause of accoustic neuromas should be close to each other.
This explains why B is correct and E incorrect.

Some more explanation on this please.

akhp77 wrote:Source: KAPLAN 800

While an extensive amount of research into the cause of acoustic neuromas have proven unsuccessful, doctors have developed new surgical options that have dramatically increased patients' survival rates.

(A) amount of research into the cause of acoustic neuromas have proven unsuccessful
(B) amount of research into the cause of acoustic neuromas has proven unsuccessful
(C) quantity of research into the cause of acoustic neuromas have proven to be unsuccessful
(D) cause research into acoustic neuromas has proven unsuccessful
(E) amount of research has proven unsuccessful into the cause of acoustic neuromas

OA: B

I have eliminated A, C and D.

What about B and E?

Research is singular so we need to use "has" and not "have". Down to B, D and E.

D changes the meaning (it widens the scope of the research). Hence incorrect.

Between B and E. Lets simplify the structure.

amount of research into the cause of acoustic neuromas has proven unsuccessful --- Research into X has proven Y

amount of research has proven unsuccessful into the cause of acoustic neuromas ---- Research has proven Y into X

Now think of it like a movie, B gives us the story and then tells us the ending (research was unsuccessful)

E breaks the flow by giving us the ending first and then giving us the background.

Hi Akhilesh,

The distinction between B and E is, as Mohit suggests, a modifier placement issue. Remember that prepositional phrases like "into the cause of acoustic neuromas" are the switch hitters of modifiers -- they can act as either adjectives or adverbs, depending on context. In this case, the prepositional phrase is an adjective modifying the noun research. What kind of research is it? It's research into the cause of acoustic neuromas.

When prepositional phrases function as adjectives and are not set off by a comma, the placement rules are pretty strict: The prepositional phrase must be as close as possible to the noun it modifies. In E, the modifier is split from it's noun by the verb "has proven unsuccessful," so the choice is incorrect. Answer B correctly places the noun, "research," and the modifying phrase right next to each other.

Make sense?

Thanks Jen