Singh, V. (1999). `O` level text-book: Module III : business systems........... Asian pub.
Lua i Stíl Chicago (17ú heag.)Singh, Vishun. `O` Level Text-book: Module III : Business Systems........... Delhi: Asian pub, 1999.
Lua MLA (9ú heag.)Singh, Vishun. `O` Level Text-book: Module III : Business Systems........... Asian pub, 1999.
Rabhadh: Seans nach mbeach na luanna seo go hiomlán cruinn i ngach uile chás.