In multipoint networks , there are tree persistence methods when a station finds a channel busy.in the 1-persistent method,after the station finds the line idle,it sends its frame immediately.this method has the （ ） chance of collision because two or more stations may find the line （ ） and send their frames immediately. In the nonpersistent method , a station that has a frame to send （ ） the line . If the line is idle , it sends immediately If the line is not idle , it waits a （ ） amount of time and then senses the line again.The nonpersistent approach （请作答此空） the chance of collision because it is unlikely that two or more stations will wait the same amount of time and retry to send simultaneously The p-persistent approach combines the advantages of the other two strategies . It reduces the chance of collision and improves efficiency.

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