https://etd.repository.ugm.ac.id/penelitian/detail/272662005never1.0https://etd.repository.ugm.ac.id/penelitian/detail/272672005never1.0https://etd.repository.ugm.ac.id/penelitian/detail/315272005never1.0https://etd.repository.ugm.ac.id/penelitian/detail/316102005never1.0