问题 单项选择题

下图为01001110的各种编码方式,不归零电平(NRZ-L)采用0表示高电平,1表示低电平。若按照从上到下的顺序,所采用的编码方式分别为()。

A.不归零电平,曼彻斯特编码,差分曼彻斯特编码,不归零1制

B.不归零电平,不归零1制,曼彻斯特编码,差分曼彻斯特编码

C.曼彻斯特编码,不归零电平,不归零1制,差分曼彻斯特编码

D.不归零1制,不归零电平,差分曼彻斯特编码,曼彻斯特编码

答案

参考答案:B

解析:

[分析]:

本题考查计算机系统硬件编码方面的基础知识。本题涉及不归零电平、不归零1制、曼彻斯特编码、差分曼彻斯特编码这几种编码方式。

不归零电平:

0=高电平

1=低电平

不归零1制:

0=在间隔的起始位置没有跳变(一个比特时间)

1=在间隔的起始位置跳变

曼彻斯特编码:

0=在间隔的中间位置从高向低跳变

1=在间隔的中间位置从低向高跳变

差分曼彻斯特编码:

在间隔的中间位置总有一个跳变

0=在间隔的起始位置跳变

1=在间隔的起始位置没有跳变

对照题中的图,编码方式分别为不归零电平、不归零1制、曼彻斯特编码、差分曼彻斯特编码。

阅读理解

MOST recently, my world has been shaken by the death of a teacher at my school. He was Dr Allan Woolley and he was only 52. Suddenly he took his own life, which remains a mystery.

That morning, everyone sensed that something wasn't right. During our lessons, an announcement was made that an assembly (集会) was scheduled for morning break, which was only done in emergencies.

Once morning break came, the entire school gathered in the main hall. As our headmaster marched out to announce the "momentous (重大的) news", it felt like the air around us trembled . Many students broke down in tears, and the reaction afterward was intensely powerful and unifying .  

The headmaster said that students were allowed to miss lessons and have a free period to collect themselves if they found the news too distressing (悲伤的). Many students went outside and shared memories of Dr Woolley to control theirselves.

Dr Woolley taught me chemistry two years ago, but up until his death he still taught many of my close friends. Many of my friends were so shocked that they still couldn't believe the person that they had owed (欠) some homework to was now dead.

It was heart-warming to spend time with teachers that morning and get to know more about them. Despite the time of sadness, I feel that every cloud has a silver lining. Although Dr Woolley's death is something nobody wanted to see, we must move on.

小题1:What did the students feel at the news of his teacher’s death?

A.unhappy   B shocked    C.surprised    D.silent

小题2:What does the underlined word “collect” in Paragraph4 mean?

A.bring something together

B.calm down

C.increase in amount

D.get and keep小题3:Which of the following is NOT true according to the passage?

A.The real cause of Dr Woolley’s death is known to us.

B.Many students didn’t prepare themselves for the bad news so that they felt very sad.

C.It takes the whole school some time to recover from the dispressing news.

D.Dr Woolley’s death allows students to understand teachers better.小题4:It can be inferred from the underlined sentences in the last paregraph that______.

A.Dr Woolley’s death made students sad.

B.There is still some comfort and hope in trouble

C.Dr Woolley’s death disappointed students greatly

D.We should forget the fact to study better.小题5:The best title for the passage should be_______.

A.Our School Faces a Tragedy

B.Dr Woolley—A Great Teacher

C.The Living Live For the Death

D.Lesson From the Death.

单项选择题