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 B)for/ until is correct as for and until mean a purpose and up to respectively. The other options are wrong as at, from, and since indicate a specific location, a source, and a duration with its starting point given a respectively. These uses don't fit in the given question. The correct answer is B)for/ until.