Adding Else into an If statement

Hi,

I have a formula that currently replys OK if it captures "C to BBNT" or "Will C SD" on Col D. However I want to add another line that gives me "NOT OK" it it is anything else. Thanks for anyones' help in advance

Public Sub NT_comment()
Dim c_ell As Range, Date_Ref As Date, S_heet As Worksheet, c_ell2 As Range

For Each S_heet In ActiveWorkbook.Sheets
If Left(S_heet.Name, 3) = "ACD" Then
    S_heet.Select
    For Each c_ell In Range("D2", Cells(Rows.Count, 2).End(xlUp))
            If c_ell = "C to BBNT" Then
                c_ell.Offset(0, 1) = "OK"
            If c_ell = "Will C SD" Then
                c_ell.Offset(0, 1) = "OK"
            End If
    Next c_ell
End If
Next S_heet
End Sub