Which party has a SIP B2BUA role in the call?

Refer to the exhibit. Which party has a SIP B2BUA role in the call?

A.
172.17.4.100

B.
10.100.4.65 and 172.17.4.100

C.
10.100.4.65

D.
None of the parties has a B2BUA role in the call.

E.
10.100.4.68 and 10.100.4.65