Private Sub Worksheet_Change(ByVal Target As Range)
If Intersect(Range("a1,c1"), Target) Is Nothing Then Exit Sub
Range("b1").Validation.Delete
If Range("a1") = "" Then
Range("b1") = ""
ElseIf Range("a1") < Range("K1") Then
Range("b1") = Range("c1")
Else
Range("b1").ClearContents
Range("b1").Validation.Add Type:=xlValidateList, AlertStyle:=xlValidAlertStop, Operator:= _
xlBetween, Formula1:="=$D$1:$D$9"
Range("b1").Select
End If
End Sub