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问题 选择题

Mary's illness ____ her absence. So don't scold her.   [ ]

A. showed      

B. accounts for  

C. explains        

D. gives out

答案

答案：B

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单项选择题

Let us now see how randomization is done when a collision occurs. After a ______, time is divided into discrete slots whose length is equal to the worst-case round-trip propagation time on the ether (2t). To accommodate the longest path allowed by Ethernet, the slot tome has been set t0 512 bit times, or 51.2μsec.

A.rest B.random C.once D.odds

After the first collision, each station waits either 0 or 1 ______ 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, or3 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 ______ 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 ______ 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 recovery is up to ______ layers.
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