The Origin attribute describes the source of the BGP prefix.
Which three are valid Origin codes?（） (Choose three.)

A. route selection
B. loop avoidance
C. determining equal cost paths for reachablilty
D. defining the application of other BGP attributes

A.MED
B.Origin
C.AS Path
D.Next Hop
E.Aggregator

A. hello
B. keepalive
C. BGP open
D. notification