InfoPath Dev

can I set show and hide base on 2 drop down list? It's not working for me.

 Hi  I try to set my drop down list base on the selection from user; when they picked American car, they'll get GM and Ford. Else, they get diff option. I'm using Rule / Set Field and get dropdown list from Sharepoint. It doesn't work. Can it be done? Thank you for your help. I'm appreciated    

hi how do I display diff fields depend on what the user pick on the car group field? Thank you for your help