开具普通发票后,发生退货或销售折让。下列说法正确的有()。A.若购货方发票未入账,购货方应将发票退还给销货方B.若购货方发票未入账,购货方无须将发票退还给销货方C.若购货方发票已入账,购货方应将发票退还给销货方D.若购货方发票已人账,购货方无须将发票退还给销货方