You can group objects to apply changes (sizing, scaling, rotating, and locking) to them as a unit. Grouping is different from selecting multiple objects, in that the changes you apply to multiple selections are applied to each object individually, while changes you apply to grouped objects are applied to the group as a unit.
Figure 1. Grouping objects 
If any of the objects you include in the group is locked, the group becomes locked, the Geometry palette becomes unavailable, and you cannot apply changes to the group. To be able to apply changes to the group, unlock the group.
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