Which approach can you use to implement IPv6-over-IPv4 tunneling?

how this would be possible ?
why not B ??

It should be “D” answer… 6PE technique can transparently transfer IPv6 packets over IP(4)/MPLS backbone (encapsulated).
Let’s think…
A. – “IPv4-compatible addressing” – Wrong. It’s NOT tunneling. It’s MAPPING.
B. – “DUAL STACK” – Wrong. Because of… It’s NOT tunneling too. This is the most desirable IPv6 implementation during the transition from IPv4 to IPv6, as it avoids the complexities of tunneling.
C. – IPsec. Wrong. You couldn’t use IPsec for non-ip traffic. Yes IPv6 is not IP. You must implement GRE OVER IPSEC for tunneling IPv6 over IPv4.
D. – It seems to be correct answer. Because in this case you are encapsulate your original IPv6 packet into the IP/MPLS packet.