Which Is the Cause of the Separation of Sister Chromatids

Multiple Choice

Which is the cause of the separation of sister chromatids during anaphase? 1.The kinetochore breaks apart
2) The spindle fibers shorten
3) The materials holding the sister chromatids degrade

A) 1
B) 2
C) 3
D) 1 and 2
E) 2 and 3