Which statement about IKE and IKE NAT-T is true?

Which statement about IKE and IKE NAT-T is true?

A. IKE is used to encapsulate ESP traffic in some situations, and IKE NAT-T is used only when the local FortiGate is using NAT on the IPsec interface. B. IKE is the standard implementation for IKEv1 and IKE NAT-T is an extension added in IKEv2. C. They both use UDP as their transport protocol and the port number is configurable. D. They each use their own IP protocol number.