selecting multiple groups I am trying to select two groups at a time. I tryed shift + G and select a group, than select another object from another group, and hit shift + G again, but the previously selected group was deselected, how can I make to select two or more groups?

thank you
Clear selection with a
All click can be done in the outliner window
In the outliner window show groups.
Click on first group 
Shift click on the second group.