Gaya APA

Ffolliott, P, F., Siregar, C, A. (2001). Natural resources management practices . Lowa: Lowa State University2001.

Gaya MLA

Ffolliott, Peter, F.., Siregar, Chairil, Anwar. "Natural resources management practices". Lowa: Lowa State University2001, 2001. Text.