2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/108947Let R be a commutative domain. We prove that an R-module B is projective if and only if Ext^1(B,T)=0 for any torsion module T. This answers in the affirmative a question raised by Kaplansky in 1962.Commutative AlgebraRings and Algebras13C10 (Primary) 13D07 16P70 (Secondary)text