信息与通信工程专业英语 教学课件 作者 徐秀兰 徐劲 李程 信息与通信工程专业英语01.ppt

（八）非限定定语从句 ① 从句中的关系代词不是直接代表它的先行词，而是对先行词作进一步的说明。如果去掉这个从句不会影响全句的主要意思。而在限定定语从句中关系代词就代表它的先行词且在从句中当主语。 ② 一般来说，非限定定语从句的前面有一个逗号，有时这个非限定定语从句还可以修饰它前面的整个句子。 ③ 对先行词的人进行说明时用who或whom。对物进行说明时用关系代词which。 ④ 关系代词which的前面还常常带有一个介词，带有介词时的关系代词就不能在从句中当主语或宾语。 例1．If the selected channel is busy, the message waits in a queue until the channel becomes free, at which time transmission begins. 例2．First the message is transmitted from the host to the message processor to which it is attached. 例3．The applications programs define the ways in which these resources are used to solve the computing problems of the users. ⑤ 有时指示代词that 也能引导非限定性定语从句。 例：The application layer differs from the other layers in that it does not provide services to any other OSI layer, but rather, only to applications outside the OSI model. 信息与通信工程专业英语 第1篇 科技书籍常用语法 It作为形式主语的主语从句 （一） 强调句型 （二） 动词不定式 （三） 分词及分词短语 （四） 非限定定语从句 （八） （一）It作为形式主语的主语从句 It + be动词（或叫系动词）+过去分词（或形容词）+ that引导的主语从句。 1．It is well known that… 众所周知…… 例：It is well known that light travels faster than sound. 2．It is said that… 据说…… 例：It is said that an asynchronous data link is character-oriented. 3．It has been found that… 人们已经发现…… It has been found that noise can be introduced into transmission path in many different ways. （二）强调句型 1．以It开头的强调句型 It +系动词（或be动词）+ 被强调的部分（谓语动词除外）+ which（或that, who）引导的从句。在如下的例句中，被强调的部分用下划线标出。 例1．It is the relationship of the true signal to the noise signal, known as the signal – to – noise ratio, which is of the most interest to the communication engineers. 例2．It was we who did an experiment on the speed of sound yesterday. 2．对于谓语动词的强调 例1．PSTN did play an important role in communication industry in the past few decades. 3．倒装语序的强调 例1．Astounding as these advances may seem, we are only at the beginning of what is possible. 例2．Each network is only capable of transporting one specific service for which it was intentionally designed. Only in a limited number of cases can it be adapted to other services. （三）动词不定式 不定式动词=