I would go with E
Although the coordination of monetary policy can help facilitate the orderly financing of existing imbalances, it is unlikely that its effect on their size is significant in the absence of an appropriate fiscal adjustment.

(A) it is unlikely that its effect on their size is significant
(B) it is unlikely that the size of their effect would be significant
(C) affecting their sizes are not likely to be significant
(D) the significance of their effect on its size is unlikely
(E) its effect on their size is not likely to be significant

A-> unlikely that is unidomatic; likely or unlikely to be is right Plus is significant says something thats happnning currently and it sounds awkward with unlikely.

B-> Same as A unlikely that plus changes meaning the size of their effect

C-> affecting their sizes are not likely to be significant -> As awkward and meaningless as it can get

D->the significance of their effect on its size is unlikely

THEIR IS PLURAL PRONOUN so cannot refer to coordination

(E) its effect on their size is not likely to be significant

its->coordination
their-> imbalances
likely to be -> IDIOMATIC

Regards,
CR

Great explanation cramya thanks

No

A is correct. E is wrong

Idiom is " it is likely that..." because something can not be likely(it is not logic to say that something is possible that)

I'd say "E"

"A" is a bit wordy, and "is" should be replaced with "would be".