Underhill, S. (1999). Twins: Steven Underhill. Gmünder.
Cita Chicago (17th ed.)Underhill, Steven. Twins: Steven Underhill. Berlin: Gmünder, 1999.
Cita MLA (8th ed.)Underhill, Steven. Twins: Steven Underhill. Gmünder, 1999.
Atenció: Aquestes cites poden no estar 100% correctes.