Cita APA (7a ed.)

Duffy, M. N. (1983). The 20th century (2. ed.). Blackwell.

Cita Chicago Style (17a ed.)

Duffy, M. N. The 20th Century. 2. ed. Oxford: Blackwell, 1983.

Cita MLA (9a ed.)

Duffy, M. N. The 20th Century. 2. ed. Blackwell, 1983.