(2000). Science: Overview, 1999. U.S. Department of Education.
Cita Chicago (17th ed.)Science: Overview, 1999. U.S. Department of Education, 2000.
Cita MLA (9th ed.)Science: Overview, 1999. U.S. Department of Education, 2000.
Atenció: Aquestes cites poden no estar 100% correctes.