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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 param_help_download(self):
        '''download XML files for parameters'''
        files = []
        for vehicle in ['APMrover2', 'ArduCopter', 'ArduPlane', 'ArduSub', 'AntennaTracker']:
            url = 'http://autotest.ardupilot.org/Parameters/%s/apm.pdef.xml' % vehicle
            path = mp_util.dot_mavproxy("%s.xml" % vehicle)
            files.append((url, path))
            url = 'http://autotest.ardupilot.org/%s-defaults.parm' % vehicle
            if vehicle != 'AntennaTracker':
                # defaults not generated for AntennaTracker ATM
                path = mp_util.dot_mavproxy("%s-defaults.parm" % vehicle)
                files.append((url, path))
        try:
            child = multiproc.Process(target=mp_util.download_files, args=(files,))
            child.start()
        except Exception as e:
            print(e)