Gaya APA
Helmer, R., Hespanhol, I. (1997).
Water Pollution Contol a Guide to The Use of Water Quality Management Principles .
London:
E & FN SPON.
Gaya MLA
Helmer, Richard., Hespanhol, Ivanildo.
"Water Pollution Contol a Guide to The Use of Water Quality Management Principles".
London:
E & FN SPON,
1997.
Text.