How let two Code List Date Type object interact

I Create first Code List Data

Second Code List Data

and define two element in BO object and enhance screen

[Label("Continents")] element CodeContinents:Codelist1Code;

[Label("City")] element CodeCity:Codelist2Code;

and enhance screen

Now, How do I let two code list data interact?

When I choose Asia, I can only see Japan and China let me choose.