Fill in the blanks with suitable prepositions:
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 D)in/ for is correct as in and for indicate a place and a duration respectively. The other options are wrong as since, at, and on indicate a duration with its starting point given, a specific location, and a surface respectively. These uses don't fit in the given question. The correct answer is D)in/ for.