The root word is movable because it can stand on it's on as a word, while "im" can not.
A pronoun can substitute a noun or a noun phrase. Among the options above only C. him and D. They are pronouns: stories is a noun and many could be a pronoun if is was standing alone, but here it is a part of a noun phrase.
C. him is singular, so the right answer is D. They
LOL. As there is 26 letters in the alphabet there is no middle !