1. There are ten stories in this book, the first four of which are the most interesting ones.

(这里为什么用of which？不是很理解of which表达的意思，把which换成them可以吗？)

答：若把 which 改为 them，则需在在逗号后使用并列连词，使之变成并列句。即：

There are ten stories in this book, the first four of which are the most interesting ones.(含定语从句的复合句)

= There are ten stories in this book, and the first four of them are the most interesting ones.(用and连接的并列句)

关于这个问题的更详细说明，请参见英语语法网上陈老师写的一篇文章：

http://www.yygrammar.com/Article/201704/5123.html 

2.May the fourth is the day which we Chinese people will never forget.

(这里为什么用 which 不用 where 呢？是因为when在句中充当时间状语，而此句中不缺状语成分吗？那 which 在这里是充当的是宾语成分吗？即：we Chinese people will never forget the day吗？)

答：这里的 which 不能改成 when 或 where，因为从句谓语动词 forget 缺宾语，而关系副词 when, where 不宜充当动词的宾语，故要用关系代词 which（作 forget 的宾语）。

3.The students will finish their education next year, by which time they will have studied here for four years.

(这里的which可以用that替换吗？这里的 which 指代的是什么呢？很难理解。)

答：这个问题与第1个问题类似，若把 which 改为 that，则需在在逗号后使用并列连词，使之变成并列句。即：

The students will finish their education next year, by which time they will have studied here for four years. (含定语从句的复合句)

=The students will finish their education next year, and by that time they will have studied here for four years. (用and连接的并列句)

4.John Adams with whose help Joe climbed the mountain, was first of the professional guides.

(这里为什么用with whose呢？原本想用who，但是发现help与climbed矛盾了，所以这里的help为名词。那么，这里的with whose是指with John Adams’s help吗?如果是这样理解的话那后面was的主语是什么呢？在网上了解到这个结构是插入语，但我怎么翻译这句话都不合理，能麻烦讲解一下成分和如何理解句意吗？)

答：是的，这里的 with whose help在意义上相当于 with John Adams’s help。后面 was 的主语是 John Adams。

5.This speech will be the reply to those whose questions have a bearing on our government's foreign policities.

(这里为什么用those whose呢？把those whose换成of whom行吗？whose在句中做什么成分呢又指代什么呢？)

答：不能把 those whose 换成 of whom。这里的 whose questions have a bearing on our government's foreign policities 是定语从句，修饰 those。