Can I list two or more atrributes in one line in a combo box, and then submit them together.
It seems that we can only display one atrribute in a combo box.
by default yes.
otherwise create a structure where you concat the attributes you want.

and perhaps there is something in the forge.

If the source of the combobox is an aggregate, you can add a new calculated attribute to it (that would contain a concat of two or more attributes) and simple use it to fill the source attribute of the combobox.