The underlined pronoun in the sentence if "whose" and it is used in the sentence as possessive. The correct option among all the options that are given in the question is the first option or option "A". The reason being that "who" would be a person that owns the phone. I hope the answer helps.
Answer: The authors choice impacts the meaning because it could change the whole story by one little move. And anything could happen within a second of the story due to the authors actions.