Howell, D. W. (1993). Passport: An introduction to the travel and tourism industry (2nd ed.). South-Western Pub.
Cita Chicago (17th ed.)Howell, David W. Passport: An Introduction to the Travel and Tourism Industry. 2nd ed. Cincinnati, Ohio: South-Western Pub, 1993.
Cita MLA (9th ed.)Howell, David W. Passport: An Introduction to the Travel and Tourism Industry. 2nd ed. South-Western Pub, 1993.
Atenció: Aquestes cites poden no estar 100% correctes.