gluNurbsCurve problem!!!!!!!!!!!!!!!!!!

I have 4 gluNurbsCurve which I am using to Trim the gluNurbsSurface.
But the problem is I have 4 sifferent nurbs curve,I have to combine
them to make them a closed loop,but every nurbs curve have there own u knots,when I combine them all
then how much knots I have to take and In which order,Given below some data of the Nurbs curve

Curve 1 :

Control Points::
(0.0,0.5 ,0.0)

U kNots:: (0.0,0.0,1.0,1.0)

Curve 2 :

Control Points::(0.0,1.0,0.0)

U kNots::(0.0,0.0,1.0,1.0)

Curve 3 ::

Control Points:: (1.0,1.0,0.0)

U kNots::(0.0,0.0,1.0,1.0)

Curve 4 ::

Control Points:: (1.0,0.5,0.0)
(0.0,0.5 ,0.0)

U kNots::(0.0,0.0,1.0,1.0)

As U can see frnd loop start with (0.0,0.5) and ends with the same point,hence creates the loop but what about the knots.
Plz any suggestions