● Let us now see how randomization is done when a collision occurs. After a __(71)__, time is divided into discrete slots whose length is equal to the worst-case round-trip propagation time on the ether(2τ). To accommodate the longest path allowed by Ethernet, the slot time has been set t0 512 bit times, or 51.2μsec. After the first collision, each station waits either 0 or 1 __(72)__ times before trying again. If two stations collide and each one picks the same random number, they will collide again. After the second collision, each one picks either 0,1,2,or 3 at random and waits that number of slot times. If a third collision occurs(the probability of this happening is 0.25),  then the next time the number of slots to wait is chosen at __(73)__ from the interval 0 to 2³-1. In general, after i collisions，a random number between 0 and 2ⁱ-1 is chosen, and that number of slots is skippeD. However, after ten collisions have been reached, the randomization __(74)__ is frozen at a maximum of 1023 slots. After 16 collisions, the controller throws in the towel and reports failure back to the computer. Further recoveryis up to __(75)__ layers。

（71）A．datagram

B．collision

C．connection

D．service

（72）A．slot

B．switch

C．process

D．fire

（73）A．rest

B．random

C．once

D．odds

（74）A．unicast

B．multicast

C．broadcast

D．interval

（75）A．local

B．next

C．higher

D．lower