You are getting the ImportCardinalityMismatchException for this line:
AskAQuestion aaq = container.GetExportedValue<AskAQuestion>();
The reason this does not work is AskAQuestion is not exported.
There are two solutions to solving the problem you want:
1) If you really want to call ComposeParts on AskSQuestion then just do that and the imports on AskSQuestion will be satisfied.
2) Add an Export attribute on AskSQuestion and just skip calling ComposeParts on it and just call GetExportedValue<AskAQuestion> to get it and it's imports satisfied.
Perhaps the thing that is confusing you right now is calling ComposeParts, what that does is simply add a particular object instance to the container and expose any exports it has as well as satisfy any imports it has.