In the following cases for quadratic convex function, which ones are correct? （ ）

A、Thestationarypointofquadraticstrictlyconvexfunctionisunique.
B、TheHessianmatrixofquadraticconvexfunctionisaconstantpositivesemi-definitematrix.
C、Thesumoftwoquadraticconvexfunctionisconvex.
D、AquadraticconvexfunctionisstrictlyconvexifandonlyifitsHessianmatrixispositivedefinite.