Fill in the blank with a suitable preposition:
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)since is correct as it indicates a duration with its starting point of time given. The other options are wrong as during, for, and at indicate a duration, a purpose, and a specific location respectively. These uses don't fit in the given question. The correct answer is C)since.