Gaya APA

Ehrlich, P, R., Ehrlich, A, H. (1972). Population resources environment : issues in human ecology (2nd ed). San Francisco: W.H. Freeman.

Gaya MLA

Ehrlich, Paul, R.., Ehrlich, Anne, H.. "Population resources environment : issues in human ecology". 2nd ed San Francisco: W.H. Freeman, 1972. Text.