code: def get_members_by_source(base_url=BASE_URL_API):
      
      url = '{}members-by-source/'.format(base_url)
      response = get_page(url)
      return response
docs: Function returns which members have joined each activity.
  
      :param base_url: It is URL: `https://www.openhumans.org/api/public-data`.