现对一些读者提出的几个关于句子分析的问题谈一些意见。
有一读者首先抄下这样一个句子：
(1)A Yale biologist said last week that genetic material known as RNA performs more functions in the body's cells than currently believed, a discovery that scientists said could alter their theories about life's earliest beginnings.
然后问到如何分析scientists said，是插入语还是定语从句？ 又，a discovery是不是that genetic material...than currently believed这一从句的同位语？
很明显a discovery只能是句中第一个that所引导的宾语从句的同位语，而不可能是其它。 至于scientists said应如何看，就需要分析了。有些英语语法书和教科书把它叫做插入语 ，似乎它并不重要，有无皆不会影响其所在的定语从句的中心思想与结构。这样分析，的确容易被人接受，不论在教的或学的方面，也都比较方便。但严格说来，这样做是不妥的。且以下面一句为例：
(2)The door was opened by a young girl who I thought at first was Tom's sister.
在这里，我们能把I thought at first看作可有可无的插入语吗？ 显然不能。因为如果将它去掉，整个从句的意思岂不由“我一开始以为她是汤姆的妹妹”一变而为“她是汤姆的妹妹”了吗？ 它既然不能叫插入语，那么应该唤作什么好呢？ 为了通俗实用起见，我们建议将它唤作定语从句中的定语从句（或复合定语从句）。形式上，它的地位似乎属于其所在的从句 ，其实并非如此。试将整个定语从句变为独立句：
(3)I thought at first that she was Tom's sister.
即可看出，I thought at first这一定语从句中的定语从句却在其所在的定语从句中起着相当于独立句中的主句作用。你看它的地位有多么重要! 好，现在再让我们回头看句（1）中的scientists said就比较清楚了。和句（2）中的I thought at first一样，它也是定语从句中的从句，不是可有可无的插入语。如果省去，不但整个that从句的意思会受到影响，而且从句中的物主代词their也没有着落了。
有一读者也抄寄一句给我们：
(4)Sometimes before the end of the decade, the sun will begin giving up its secrets—that is, if a new orbiting device called Solar Optical Telescope （SOT）works the magic that scientists think it will.
然后问道： ① that scientists think it will是什么成分？ ② scientists think是不是插入语？ ③ it will中的it代表什么？ 是否代表SOT?
我们认为，that scientists think it will显然是定语从句，修饰the magic。scientists think和句（1）中的scientists said一样，不是插入语，而是定语从句中的定语从句。it will是省略结构，后面省去了前面已用过的work magic，代词it代表a new orbiting device，也就是SOT.
一位读者来信问到如何分析下列句中的like a spoon和不定式to promise与to forget:
(5)The earliest compass was shaped like a spoon.
(6)A man apt to promise is apt to forget.
在分析介词短语like a spoon之前，我们最好先将句（5）的被动结构还原为主动结构如下 ：
(7)They shaped the earliest compass like a spoon.
在这个主动句中，like a spoon显然是宾语compass的补足语。在被动句中，compass变成了全句的主语，但like a spoon仍是它的补足语，不过已不是宾语补足语而是主语补足语了。
关于句（6）中形容词apt后的不定式问题，可参看本书题为《几个有关形容词的问题》中的第四个问题。和对待（8）I'm glad to see you.
中形容词glad后的不定式to see一样，可以把apt后的to promise与to forget看作宾语， 也可以把它们看作状语。但我们愿意重复一下： 在这种情况下，最好的学习方法不是进行句子分析，而是将它作为一种句型来掌握。这个句型就是“主语+连系动词+形容词+不定式”。下面按此句型再介绍几个常用的句子，供读者参考：
(9)Are you able to come?
(10)I'm always ready to help.
(11)He is not likely to come.
(12)She is quick to learn.
(13)It's sure to rain.
(14)I'm sorry to see you leave.
(15)I'd be happy to help you.
(16)He's very anxious to please.
(17)He is always eager to win.
(18)The children are impatient to start.
(19)She's quite content to sit and read a book.
(20)You're not afraid to go alone, are you?
有一位读者抄寄来一个长句如下：
(21)Jonas had told them how the meat that was taken out of pickle would often be found sour, and how they would rub it up with soda to take away the smell, and sell it to be eaten on free-lunch counters; also of all the miracles of chemistry which they performed, giving to any sort of meat, fresh or salted, whole or chopped, any color and flavor and odor they chose.
问如何分析and sell it to be eaten on free-lunch counters, of all the miracles中的of，以及giving to any sort of...any color and flavor...的功用。
连词and连接sell和前面的动词rub，这两个动词共用一个情态动词would（也可以说sell前省去了would）; to be eaten是表结果（状语）的被动不定式；on free-lunch counters是地点状语，修饰to be eaten。介词短语of all the miracles中的of与前面的两个how引导的宾语从句并列，also of...= Jonas had also told them of all the miracles...分词短语giving to any sort of...是修饰miracles的非限制性定语。
