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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 origination_urls(self):
 """ Access the origination_urls :returns: twilio.rest.trunking.v1.trunk.origination_url.OriginationUrlList :rtype: twilio.rest.trunking.v1.trunk.origination_url.OriginationUrlList """

        if self._origination_urls is None:
            self._origination_urls = OriginationUrlList(self._version, trunk_sid=self._solution['sid'], )
        return self._origination_urls