The correct option is B Down
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 B)down is correct as it is used to express a firm position. The other options are wrong as below is used to indicate a position lower than something, beneath is used to indicate that something is under the other, and in is used to indicate a place in an area. These uses don't fit in the given question. The correct answer is B)down.