DatafileDF1belongstotablespaceTS1.，andthedatabaseisinARCHIVELOGmode.Youdidanincompleterecoverinthefollowingsteps：1.TakedatafileDF1offline.2.CopyabackupcopyofDF1intothecurrentDF1location.3.ExecuteRECOVERDATAFILEUNTILTIMEsometimeinthepast.4.BringDF1online.5.ExecuteALTERDATABASEOPENRESETLOGS.Toguaranteethatthedatabaseisrecoverableinthefuture，whatistheleastamountofworkneeded？（）

A.Backupthedatafile.

B.BringtablespaceTS1online.

C.Copyredologstothebackupdirectory.

D.Makeacompletebackuprightafteropeningthedatabase.