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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 _add_eutils_api_key(url):
 """Adds eutils api key to the query :param url: eutils url with a query string :return: url with api_key parameter set to the value of environment variable 'NCBI_API_KEY' if available """

    apikey = os.environ.get("NCBI_API_KEY")
    if apikey:
        url += "&api_key={apikey}".format(apikey=apikey)
    return url