IMO...C...

Explanation:
Federal agricultural programs aimed at benefiting one group whose livelihood depends on farming often end up harming another such group.

Case 1:
An effort to help feed-grain producers resulted in higher prices for their crops, but the higher prices decreased the profits of livestock producers.
Group benefited = feed-grain producers
Group harmed = livestock producers

Case 2:
In order to reduce crop surpluses and increase prices, growers of certain crops were paid to leave a portion of their land idle, but the reduction was not achieved because improvements in efficiency resulted in higher production on the land in use.
Since the reduction in crop surplus didn't happen, ideally this case doesn't given any benefit of a group on the cost of another group's harm!

Case 3:
Many farm workers were put out of work when a program meant to raise the price of grain provided grain growers with an incentive to reduce production by giving them surplus grain from government reserves
Group benefited = Grain growers - They got the grains without actually growing them
Group harmed = Farm workers - No employment as no grains were actually grown.

hence case 1 and case 3 support the claim in the question.

jeeteshsingh ...very good explanation
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III can't be right because even if people out of work is the group getting harmed, "government reservoir" is certainly NOT the "benefiting group whose livelihood depends on farming". So, I think A. Experts, please explain why or why not.
thanks in advance.

interesting question, but 2 things.
1/ this question is not hard.
2/ the style does not look like a gmat question.

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