If R1 is configured for 6to4 tunneling, what will the prefix of its IPv6 network be?

Refer to the exhibit. If R1 is configured for 6to4 tunneling, what will the prefix of its IPv6 network be?

A.
1723:1100:1::/48

B.
FFFF:AC1F:6401::/16

C.
AC1F:6401::/32

D.
2002:AC1F:6401::/48

E.
3FFE:AC1F:6401::/32