2 questions~about triangle!!!!!!!!!!!

each of the following cases lists the lengths of three line segments. Which set of line segments cannot form a triangle?
A. 15cm,7cm,9cm
B.6cm,14cm,10cm
C.13cm,28cm,14cm
D.10cm,13cm,22cm

the circumcentre of a triangle is the point of intersection of the three
A.angle bisectors
B.medians
C.altitudes.
D.perpendicular bisectors