Confusing SC question

[dpatwa]

Recent cosmological advances have made it possible to observe stellar objects that would only a decade ago have been unable to be viewed.

A - it possible to observe stellar objects that would only a decade ago have been unable to be viewed
B - it possible to observe stellar objects that would have been invisible only a decade ago
C- possible that one can observe stellar objects invisible only a decade ago
D- possible the observing of stellar objects that were not capable of being viewed only a decade ago
E- possible the observing of stellar objects that only a decade ago would not have been able to be viewed

I'm having trouble with understanding why the correct answer is listed as B. I chose E. In B, I don't think "it" unambiguously refers to a noun.

Source- Princeton Review

[jayhawk2001]

Purpose is best denoted by "to + verb"

C, D and E lack the structure to denote this purpose.

A has awkward construction.

[800GMAT]

In B, I don't think "it" unambiguously refers to a noun.

In such sentences 'it' need not have a pronoun reference

Following are examples from OG:

1.It is possible that Native Americans originally migrated to the Western hemisphere over a bridge of land that once existed between Siberia and Alaska
2.It is well known in the supermarket industry that how items are placed on shelves and how frequently the inventory turns over can be crucial to profits.

[mayonnai5e]

Recent cosmological advances have made it possible to observe stellar objects that would only a decade ago have been unable to be viewed.


E- possible the observing of stellar objects that only a decade ago would not have been able to be viewed

When using the idiom "have made possible," a noun is required to show what was being made possible --> "have made possible the observation" and not "have made possible the observing" (which uses a verb)

[sogmat]

to me B changes the meaning of the sentence so i chose A though it seemed grammatically incorrect

[vittalgmat]

E is very wordy and ackward.
B is the best.