为了使物理层在实现1000Mbps速率时所使用的传输介质和信号编码方_爱下问搜题

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问题单项选择题

为了使物理层在实现1000Mbps速率时所使用的传输介质和信号编码方式的变化不会影响( )，IEEE 802.3z标准调整了物理层。

A．网络层

B．LLC子层

C．MAC子层

D．表示层

答案

参考答案：C

解析： IEEE 802.3z标准在LLC子层使用IEEE802.2标准，在MAC子层使用CSMA/CD方法，只是在物理层作了一些调控，定义了新的物理层标准1000BASE-T。1000BASE-T标准采用千兆介质专用接口 (GMII)，它将MAC子层与物理层分隔开来，使得物理层在实现1000Mbps速率时所使用的传输介质和信号编码方式的变化不会影响MAC子层。

完形填空

After the birth of my second child, I got a job at a restaurant. Having worked with an experienced 16  for a few days. I was 17  to wait tables on my own. All went   18  that first week. When Saturday night came, I was luckily 19  the tables not far from the kitchen. 20 , I still felt it a little hard to carry the heavy trays(托盘).
Before I knew it, the   21  was full of people. I moved slowly,   22  every step. I remember how 23  I was when I saw the tray stand near the tables; it looked different from the one I was   24  on. It had nice handles, which made it 25  to move around. I was pleased with everything and began to   26  I was a natural at this job.
Then, an old man came to me and said, “Excuse me, dear, my wife and I loved   27  you work. It seems your tray stand has been very   28  to you, but we are getting ready to   29  now, and my wife needs her 30  back.”
At first his 31  did not get across. “What was he talking about!” Then, I got it. I had set my trays on his wife’s orthopedic walker(助步器). I stood frozen as ice, but my face was   32 . I wanted to get into a hole and   33 .
Since then, I have learned from many mistakes such as the one I just  34 . I have learned to be more   35  and not to be too sure of myself.

D．interesting

B．full of joy

判断题

桩孔成型后，当暂不浇注混凝土时，孔口必须及时封盖。