Want combo 2 b null for new record

[Faraz A. Qureshi]

I have a subform with a combobox derived from a query like:
SELECT COA.AcNo, COA.Acc, COA.Cl FROM COA WHERE
(((COA.Cl)=[Forms]![Clnt]![SetAc].[Form]![ID]));

So as to allow limited number of options depending upon the type of customer
of the selected.

However, when I launch the main form I want the subform's said field to be
showing a blank for a new record instead of showing the first item.

Any idea?