Cita APA (7a ed.)

Duffy, M. N., & Gell, K. (1965). The 20th century (3. impression.). Blackwell.

Cita Chicago Style (17a ed.)

Duffy, M. N., y Kathleen Gell. The 20th Century. 3. impression. Oxford: Blackwell, 1965.

Cita MLA (9a ed.)

Duffy, M. N., y Kathleen Gell. The 20th Century. 3. impression. Blackwell, 1965.