conservation for art is "preserving, fixing, or just restoring old art or other things like artifacts etc." (found in an article on www.msaconservation.com) it's most likely controversial because if something's old and valuable, people want to keep it in it's original form. (just a guess) but that's how it is in the art world.
Art can serve a purpose in religious buildings simply in the architecture itself. Also, art can be a constant reminder of one's religious beliefs.
The answer to your question is C
