using RowSource property but nothing appear in Combo box

Hi,

i am using the RowSource property to display values in a ComboBox, however, the values is not displayed but i am not sure why. Below is an extract of the code, would really appreciate if anyone can tell me the problem.

Private Sub ComboET2_Change()
Dim wss As Worksheet
Set wss = Sheets("ET")
   
If Trim(Me.ComboET1.Value) = wss.Range("A2").Value And Trim(Me.ComboET2.Value) = wss.Range("B2").Value Then
ComboET3.RowSource = "c2: c14"
    Else
    If Trim(Me.ComboET1.Value) = wss.Range("A2").Value And Trim(Me.ComboET2.Value) = wss.Range("B15").Value Then
    ComboET3.RowSource = "c15:c26"
    End If
End If

If Trim(Me.ComboET1.Value) = wss.Range("A27").Value And Trim(Me.ComboET2.Value) = wss.Range("B27").Value Then
ComboET3.RowSource = "c27:c36"
    Else
    If Trim(Me.ComboET1.Value) = wss.Range("A27").Value And Trim(Me.ComboET2.Value) = wss.Range("B37").Value Then
    ComboET3.RowSource = "c37:c40"
    End If
End If

Thanks.