单选题：For purposes of behavior modeling an event occurs whenever __.

For purposes of behavior modeling an event occurs whenever __. @[B](1)

A. a state and process exchange information.
B. the system and an actor exchange information.
C. two actors exchange information.
D. two objects exchange information.




A.a state and process exchange information.
B.the system and an actor exchange information.
C.two actors exchange information.
D.two objects exchange information.


答案：B