Which are the two packets that are used in WCCP discovery process?

Which are the two packets that are used in WCCP discovery process? (Choose all that apply)

(a) HERE_I_AM
(b) HOME_ROUTER_IP:
(c) I_SEE_YOU
(d) WEB_CACHE_HERE

A.
All of the above

B.
a, b & c only

C.
b & d only

D.
a & c only

Explanation: