Adding the 2nd and 3rd condition

My form has a combobox with 3 choices in it: No, Yes, Unknown. If one
selects no, an input form pops up for one to enter a new Acct address
information. If the user selects Yes, then the address information is
supposed to be the same as the persons mailing address. If the person
selects unknown, then my report will have a statement "There was address
provided for the acctount"

how will I add the Yes part code and the unknown part code on my form.
if there is no need for the unknown code in my form then how will I put tha
information in my report?

Private Sub AcctDescrAvailable_AfterUpdate()
Dim strARG As String
Dim strSQL As String
Dim DocName As String
Dim LinkCriteria As String
Dim Response As Integer
Dim Cancel As Boolean

DoCmd.DoMenuItem acFormBar, acRecordsMenu, acSaveRecord, , acMenuVer70

If AcctDescrAvailable.Value = "No" Then
strARG = _
"Account Information, SELECT MailAddressLine1 as
AcctAddrLine1,MailAddressLine2 as AcctAddrLine2, propCity as AcctCity,
MailState as AcctState,MailZipCode as AcctZipCode FROM tblAcctInfor where
[AcctID] = " & AcctID & ";"
DocName = "frmAcctDescInput"
DoCmd.OpenForm DocName, , , LinkCriteria, , , strARG
Else
strSQL = "UPDATE tblAcctInfor SET MailAddressLine1, MailAddressLine2,
MailCity, MailState, MailZipCode= null where [AcctID] =" & AcctID & ";"
CurrentDb.Execute strSQL
End If

End Sub