Singh, V. (1999). `O` level text-book: Module III : business systems........... Asian pub.
Chicago-čujuhus (17. p.)Singh, Vishun. `O` Level Text-book: Module III : Business Systems........... Delhi: Asian pub, 1999.
MLA-čujuhus (9. p.)Singh, Vishun. `O` Level Text-book: Module III : Business Systems........... Asian pub, 1999.
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