Solutions:
(a) O is a common point between ∠COD and ∠AOB
(b) O and B are common points between ∠AOB and ∠BOC
(c) O, E and B are common points between ∠AOB and ∠BOC
(d) O, E, D and A are common points between ∠BOA and ∠COA
(e) OC is common ray between ∠BOC and ∠AOC