import re


def clean_text(text: str):
    """
    Applies basic pre-processing to clean a sentence
    :param text: (str) A string of text that contains the movie title and description
    :return: text: (str) Input string with only characters of the alphabet
    """
    text = text.replace("_", " ")  # replace underscores with space
    text = re.sub("\'", "", text)  # remove backslash-apostrophe
    text = re.sub("[^a-zA-Z]", " ", text)  # remove everything except alphabets
    text = ' '.join(text.split())  # remove whitespaces
    text = text.lower()  # convert text to lowercase

    return text