import re


def remove_marks(text):
    """
    Remove those unnecessary marks inside texts.

    Arg:
        text: A string that could be either posts or comments.
    Return:
        new_text: A string which is a clean sentence.
    """
    # remove HTML tags 
    new_text = re.sub('<.*?>', '', text) 

    # remove URL
    new_text = re.sub('http\S+', '', new_text)  

    # replace number with <NUM> token
    new_text = re.sub('\d+', ' NUM ', new_text)

    return new_text