Join 3D Polylines

[advandes]

I have an AutoCAD file with 3D Polylines and I can't figure out how to join them so I can extrude the 2D shape at the bottom along the entire path. I have attached the file. Any help would be very much appreciated.

[Shneuph · Accepted solution]

I just selected them all and typed "JOIN" and it combined them into 4 3d polylines in AutoCAD 2016