Himu -
Mission 2012 is right. The way that it is currently worded C is not the best, but only because of the use of the word "elected" as in "elected officials."
Now, I can guarantee you that based on this information, I will get this question edited and it will no longer say "elected officials" but will just say "officials."
Now with that change made, the answer is C. This is surprising because B is what you are looking for and B is a pretty good answer.
Neha - Mission is right, B is not incorrect because of the possibility of switching parties, the stimulus does say that what matters is what political party the DA belonged to "When she took office."
The reason that the answer is C is that with the correction mentioned, C is even better! You see, with choice B we still have the possibility that even though the Federal Party gets to choose the replacement, they may not choose a member of their own party. The fact is that we do not know that the Federal Party will nominate a member of the Federal Party to be DA. It seems logical, but it is not as good as C. If C where not available this would be the answer since it only requires the assumption that the Federal Party appoints District Attorneys from the Federal Party.
But if we correct C it requires no assumptions! It literally guarantees that they appoint a member of the Federal Party. So this is tricky - B is what you anticipate, but once C is edited of that one word, C is better!
Does that make sense?
So Mission, thanks very much for pointing that out to me I will get it changed. So that now we can deal with Choice C as it should be written without "elected" officials. And I think that you will agree that now C is unexpected, but better.