https://etd.repository.ugm.ac.id/penelitian/detail/539642012never1.0https://etd.repository.ugm.ac.id/penelitian/detail/540192012never1.0https://etd.repository.ugm.ac.id/penelitian/detail/552322012never1.0https://etd.repository.ugm.ac.id/penelitian/detail/711562012never1.0