Fill in the blank with a suitable option:
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 is correct as it indicates help. The other options are wrong as in, out, and at indicate the inside of something, away from the inside of something, and a specific location respectively. These uses don't fit in the given question. The correct answer is B)for.