With respect to address summarization, which of the following statements concerning IPv4 and IPv6 is true?

A.
The potential size of the IPv6 address blocks suggests that address summarization favors IPv6 over IPv4.

B.
Role based addressing using wildcard masks to match multiple subnets is suitable for IPv4, but unsuitable for IPv6.

C.
In order to summarize, the number of subnets in the IPv4 address block should be a power of 2 while the number of subnets in the IPv6 address block should be
a power of 64.

D.
WAN link addressing best supports summarization with a /31 subnet for IPv4 and a /126 for IPv6.

Explanation:
http://www.ciscopress.com/articles/article.asp?p=1763921
“For IPv6 access lists, the wildcard masks are not usually used. All source and destination addresses are notated in the form of prefixes. Therefore, it is important
that subnets that are to be grouped in an access list falling within a summarized address range.”