e.g: health journal, business article, american soldier.
51 DAFTAR PUSTAKA Akbar, F. , (1996), "Sintesis Zeolit A dari Abu Layang Batubara", Thesis Program Pasca Sarjana , Universitas Gadjah Mada, Yogyakarta.
http://digilib.its.ac.id/public/ITS-Undergraduate-10935-Bibliography.pdf