This has also resulted in an increase in the sheer number of advertisements towhich audiences are exposed.

　　英语四级译文:

　　这也使得观众能看到的(电视)广告的数量大量增加。

　　四级词汇讲解:

　　本句的主干是this has also resulted in an increase 。to which audiences are exposed是由“介词+关系代词”引导的定语从句，修饰先行词advertisements。

　　sheer的意思是“完全的，十足的”，表示幅度大;sheer number指“巨大的数量”。be exposed to的意思是“接触;面临”。

　　英语四级考点归纳:

　　由“介词+关系代词”引导的定语从句须注意的几个问题。

　　关系代词which和whom在定语从句中作介词的宾语时，介词可放在关系代词之前，也可放在该定语从句中的动词之后(此时，which可用that代替，whom可用who或that代替。在口语和非正式文体中，关系代词可以省略)。如:

　　On the isolated island, there wasn't a single person to whom she could turn for help.在这座孤岛上，没有一个她可以寻求帮助的人。

　　此句可以改为:

　　On the isolated island，there wasn't a single person(who/whom/that)she could turn to for help.

　　关系代词that在定语从句中作介词的宾语时，介词只能放在从句中相关动词之后，不可放在that前面，但that可省略。如:

　　1) The house ( that ) we live in is not large。我们住的房子不大。(√)

　　2)The house in that we Iive is not large.(×)

　　在由“代词+of+关系代词”结构引导的定语从句中，先行词指“人”时用whom，指“物”时用which。如:

　　1) There are 50 students in my class, most of whom are girls.我们班上有50个学生，其中大多数是女孩。

　　2)Finally he finished the paper, most of which was downloaded from the lntemet.最后他终于完成了论文，但大部分是从网上下载的。