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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def clean_abstract(abstract, remove_tags=['xref', 'ext-link', 'inline-formula', 'mml:*']):
 """ Remove unwanted tags from abstract string, parsing it as HTML, then only keep the body paragraph contents """

    if remove_tags:
        for tag_name in remove_tags:
            abstract = utils.remove_tag(tag_name, abstract)
    return abstract