Dynamic refresh dropdown list

I have a selection form with multiple dropdown lists, let's say A, B and C. If the dropdown list B is changed, then dropdown list C should be updated. To get this done, I use a small javascript function reload(form) { var val=form.B.options[form.B.options.selectedIndex].value; self.location='myForm.php?B=' + val ; } called by <select id="B" name="B" onChange="reload(this.form);"> This works fine, BUT all other dropdown lists are also reset. So if I select another A, then another B, then also A is reset to its prior value. Any idea how I can refresh a specific dropdown, without affecting all the other dropdowns ? TIA, Cor