Which as-path access-list regular expression should be applied on R2 as a neighbor filter
list to only allow updates with an origin of AS 65503?
Refer to the exhibit.

A.
_65503.?$

B.
^65503 .*

C.
65503

D.
_65503_

E.
_65503$

F.
^65503$

Explanation:
http://www.cisco.com/c/en/us/td/docs/ios/12_2/termserv/configuration/guide/ftersv_c/tcfaapre.html