Source of the question: self made

Some policies that were abrogated in the congress last year were established in violation of the provincial human rights.
(A) Some policies that were abrogated in the congress last year were
(B) Some policies that were abrogated in the congress last year have been
(C) Some policies that were abrogated in the congress last year had been
(D) Last year the congress abrogated some policies that have been
(E) Last year some of the policies that were abrogated in the congress had been
(F) Some of the policies that were abrogated in the congress last year had been

Please clarify the following doubts:
1. Is there any difference between some policies and some of the policies; kindly explain which choice is correct (C) or (F)
2. Is Last year acting as "adjective phrase" in Choice E and as "adverbial phrase" in other choices. If yes, could you please explain how ?

Many Thanks in Advance

'some policies' is just indefinite: it implies nothing about how many policies there were, whether these policies constituted a significant fraction thereof, or whether some reference set of policies has already been mentioned.
'some of the policies' implies that there is some known set of policies (i.e., the policies) from which we're choosing. it's a subtle difference, but there's an implication that the reader is at least aware of the general scope and extent of 'THE policies'.

c vs. f would therefore depend on the larger context within which this sentence was found, and would not appear simultaneously on the same gmat question. (btw, i know which OG question you've modeled this one on; choice f is an add-on which doesn't have a corresponding answer on that question)



'last year' is adverbial in both cases: it describes the time frame of an action, and therefore modifies the verb whose time frame it clarifies.
the problem with choice e, though, is that it changes the fundamental meaning of the sentence. the original sentence says that the policies were abrogated last year, and that they had previously been enacted in violation of human rights. however, if you eliminate the modifier, the 'skeleton' of choice e says that
Last year some of the policies ... had been established ...
that's unacceptable, because the policies weren't established last year (that's when they were abrogated).