Class distribution problem

[Daok]

What is the best way to have some function in a tree or inherate class.

Here is what I have :

ClassA (who have the main)                     --
    |___ClassB (object 1)                             |----ClassD
                 |____ClassC (object 2)            --

And I want all to have ClassD but I do not want to include ClassD in all Class.

[Daok]

I think it's something that all know... is there a way or not ?