You can append:
If the ends of the two objects do not join, a span is added to the ends.
To append a curve:
If you are appending to a composite curve, any wireframe object can be selected. If appending to a curve, only a curve can be selected.
The next to Select object to append changes to .
By default, the ends of the objects nearest to each other are appended. If the two ends don't touch, they are joined by a span. The tangency at the ends of the new span matches the ends of the existing objects:
As you click Next, the other solutions are displayed on the screen.