Question 1072859
None.


Attach length of 2 to one endpoint of the 7 cm segment and attach the length 4 to the other endpoint of the 7 cm segment.  Rotate the two pieces to connect them together.  They will not meet.  If you cannot make the loose ends of the lengths 2 and 4 meet, then no triangle is formed.  


(Also look for information about Triangle Inequality Theorem.)