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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 get_members_by_source(base_url=BASE_URL_API):
 """ Function returns which members have joined each activity. :param base_url: It is URL: `https://www.openhumans.org/api/public-data`. """

    url = '{}members-by-source/'.format(base_url)
    response = get_page(url)
    return response