To Combine Curves
You can combine two end-to-end curves a into a single curve. One curve must have a soft point on the other curve. The combined curve changes shape to maintain smoothness.
If the two curves have different curve degrees, the resulting combined curve has the highest curve degree.
However, low degree (1, 2) curves are different. Combining low degree curves will elevate the degree of the resulting curve.
1. In the Model Tree, right-click the Style feature that contains the curve to combine, and choose 
Edit Definition. The Style tab opens.
Edit Definition. The Style tab opens.2. Click > 
Curve Edit. The Curve Edit tab opens.
Curve Edit. The Curve Edit tab opens.3. Under Curve, click the 
collector, and select a curve.
collector, and select a curve.4. Right-click the endpoint of the selected curve and choose Combine from the shortcut menu.
If there is more than one neighbor curve at the endpoint, you are prompted to select which curve to combine with the selected curve.
5. Click 
OK.
OK.