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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_vts_xml(self, vt_id=None, filtered_vts=None):
 """ Gets collection of vulnerability test information in XML format. If vt_id is specified, the collection will contain only this vt, if found. If no vt_id is specified, the collection will contain all vts or those passed in filtered_vts. Arguments: vt_id (vt_id, optional):
 ID of the vt to get. filtered_vts (dict, optional):
 Filtered VTs collection. Return: String of collection of vulnerability test information in XML format. """


        vts_xml = Element('vts')

        if vt_id:
            vts_xml.append(self.get_vt_xml(vt_id))
        elif filtered_vts:
            for vt_id in filtered_vts:
                vts_xml.append(self.get_vt_xml(vt_id))
        else:
            for vt_id in self.vts:
                vts_xml.append(self.get_vt_xml(vt_id))

        return vts_xml