A preposition is a word which comes before a noun or a pronoun and establishes a relationship between the elements of a clause or words. Option C)for is correct as it is used to express a purpose. The other options are wrong as off with, out, and up is used in exhortations to take or send someone in or out, to indicate a position away from inside, and a position above something respectively. These uses don't fit in the given question. The correct answer is C)for.