Economic theory fails to explain the extent to which

[raj44]

Economic theory fails to explain the extent to which savings from personal income has shifted to short term bonds, money-market funds, and other near term investments by the instability in the futures market.

1. to which savings from personal income has shifted
2. of savings from personal income that has been shifted
3. of savings from personal income shifting
4. to which savings from personal income have shifted
5. to which savings from personal income have been shifted

I feel the answer must be D instead of E since the purpose of the sentence is served by the present perfect tense and there's no need to use the perfect continuous tense?

Experts please comment.

[MartyMurray]

This is one of those which require a careful reading of the entire sentence.

Notice this toward the end of the sentence.

by the instability in the futures market

That prepositional phrase makes the original sentence weird. It's not clear what is even supposed to be going on.

We can simplify the situation by cutting out part of the original sentence to get this.

Economic theory fails to explain the extent to which savings from personal income has shifted...by the instability in the futures market.

Choice D would create this essentially.

Economic theory fails to explain the extent to which savings from personal income have shifted...by the instability in the futures market.

We are still stuck with the prepositional phrase by the instability futures market, and the sentence does not work.

Now, if we add a been, as provided by choice E, we get this.

Economic theory fails to explain the extent to which savings from personal income have been shifted...by the instability in the futures market.

Now the sentence works in its entirety. Choose E.