(第3空)CSMA,although more efficient than ALOHA or slotted ALOHA,still has one glaring inefficiency.If the medium is busy,the station will wait for a random amount of time. When two frames collide,the medium remains ( ) for the duration of transmission of both damaged frames. The use of random delays reduces the probability of ( ). For ( ) frames,compared to propagation time,the amount of wasted capacity can be considerable.This waste can be reduced if a station continues to listen to the medium while( ).The maximum utilization depends on the length of the frame and on the( ) time; the longer the frames or the shorter the propagation time，the higher the utilization..