http://repository.usu.ac.id/xmlui/bitstream/handle/123456789/19701/Chapter%20I.pdf?sequence=5
http://repository.usu.ac.id/xmlui/bitstream/handle/123456789/19701/Chapter%20II.pdf?sequence=4
http://repository.usu.ac.id/xmlui/bitstream/handle/123456789/19701/Reference.pdf?sequence=2