GUTH, H. P., & SHNIDER, P. S. (1981). Our world today. D.C. Heath.
Cita Chicago (17th ed.)GUTH, Hans P., i Patricia S. SHNIDER. Our World Today. Lexington: D.C. Heath, 1981.
Cita MLA (9th ed.)GUTH, Hans P., i Patricia S. SHNIDER. Our World Today. D.C. Heath, 1981.
Atenció: Aquestes cites poden no estar 100% correctes.