How can I display a question with compound answers?

I've got to display to the user options to set a value into one of four states:

• A1
• A2
• B1
• B2

Is it better to have a radio button enumerated as above or two sub questions:

• A or B?
• 1 or 2?

and then combine them behind the scenes?

These options could be phrased to allow either two pairs of radio buttons or two checkboxes so I'm not really interested in that aspect. The question is whether we have a single question with four choices or two questions each with two choices.

It has been decided, by someone else, that this is to be stored as a single value and so I can't easily change this without having a serious knock on effect in the system.