A Carrier Sensing Multiple Access / Collision Detection ( CSMA / CD ) network has four stations A , B , C , D . Suppose station A needs to transmit a frame after 2 collision, station needs to transmit a frame after 3 collision, station needs to transmit a frame after 4ℎ collision, and station needs to transmit a frame after 5 ℎ collision, what is the probability that each station will choose a different random integer value for determining the backoff time?