[AccessD] Add All to List

How do you add All to List? This form contains 2 combo boxes on a main form.
Selecting data shows data on a subform for the related combo box choices.

I need to either have an All in the combo boxes or when the form opens, I
would like them to be blank.

 I tried this code in the On Open of the main form, but it still opens to
the first record with entries in both combo boxes.

    With Me
        .cboNCSANo = ""
        .cboProcedure = ""
    End With

Virginia