Which two BGP attributes must be supported by all BGP implementations and must be included...

BGP attributes are properties that BGP uses for route advertisement, path selection, and loop prevention 1 .  There are four categories of BGP attributes 1 2 3 :

Well-known mandatory: Must be recognized by all BGP routers, present in all BGP updates, and passed on to other BGP routers 1 2 3 .

Well-known discretionary: Supported by all BGP implementations, and are optionally included in BGP updates 1 .

Optional transitive: May not be supported by all implementations of BGP 1 .

Optional non-transitive: May not be supported by all implementations of BGP 1 .

The well-known mandatory attributes must be supported by all BGP implementations and must be included in every update 1 2 3 .  These include the AS path and next hop attributes 2 3 . Therefore, options A and C are correct.