Gaya APA

Keefer, R, F., Sajwan, K, S. (1993). Trace Elements in Coal and Coal Combustion Residues : Advances in Trace Subtances Research . Boca Raton: Lewis Publishers.

Gaya MLA

Keefer, Robert, F., Sajwan, Kenneth, S.. "Trace Elements in Coal and Coal Combustion Residues : Advances in Trace Subtances Research". Boca Raton: Lewis Publishers, 1993. Text.