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 A)in is correct as it indicates that something is a part of the other. The other options are wrong as on, at, and over indicate a surface, a specific location, and completion of task respectively. These uses don't fit in the given question. The correct answer is A)in.