def find_pronoun(sent):
    """Given a sentence, find a preferred pronoun to respond with. Returns None if no candidate
    pronoun is found in the input"""
    pronoun = None

    for word, part_of_speech in sent.pos_tags:
        # Disambiguate pronouns
        if part_of_speech == 'PRP' and word.lower() == 'you':
            pronoun = 'I'
        elif part_of_speech == 'PRP' and word == 'I':
            # If the user mentioned themselves, then they will definitely be the pronoun
            pronoun = 'You'
    return pronoun