Sometimes you can click on the button under the "A", which is "Link to parent" which will allow you to Group objects and Groups of groups. Be careful to back up just before you do that Sometimes it changes the heirarchy of groups and can change Booleaned shapes. Simplest method I've found is dragging a marquee selection around all the objects, also different sets of groups with out the danger of changing their boolean properties. One small note here, sometimes it's difficult to get a clear area to drag around with out effecting neighboring objects. The fix on that is to lock those neighbors. I know it seems like a lot of stuff just to get your thumbnails to show, but after a a few times you won't even give a second thought, it'll just come natural. ICM

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Ockham's razor- It's that simple