Fill in the blank with the most appropriate word.
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) to become is correct as it indicates a direction. The other options are wrong as become, of becoming, and becoming indicate that the given sentence doesn't require a preposition, of indicates possession, and becoming is a process respectively. These uses don't fit in the given question. The correct answer is B)to become.