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From SofTutor for AutoCAD 3D - Grouping Staircase With Object Grouping
Topics covered in this video are:

Zoom Window Command Detail Model Close Up
Grouping Staircase With Object Grouping 3D Duplicate Demo
Remove, Add, And Crossing To Group Elements Object Name Demo
HIGHLIGHT Tool In Object Grouping Indicate Show Demo
ADD Tool In Object Grouping Select Name Demo