(1972). The World of learning, 1971-72 (22nd edition.). Europa.
Cita Chicago Style (17a ed.)The World of Learning, 1971-72. 22nd edition. London: Europa, 1972.
Cita MLA (8a ed.)The World of Learning, 1971-72. 22nd edition. Europa, 1972.
Precaución: Estas citas no son 100% exactas.