Which description of OpFlex is true?

Which description of OpFlex is true?

A.
a proprietary protocol that is used for communication between ACI spine and leaf

switches

B.
a Cisco protocol that is used between third-party orchestration tools and Cisco APIC

C.
an open and extensible policy protocol for transferring policy between a network policy
controller and any device

D.
an open protocol that is used between virtual machine managers and ACI leaf switches
to transfer VXLAN-encapsulated packets