句子的同位语多由名词短语充当，但少数词之后可接由that引导的从句作同位语，此时需和定语从句相区别，同位语从句中that不在从句中承担成分，而且不可省略

　　如：I was disillusioned by the fact that he had deserted us for ever.

　　The idea that man is inferior to animals is quite unacceptable.

　　可接同位语从句的名词有：fact, reason, idea, news, hope, doubt, belief, proof等

　　例题：

　　(1)

　　Astronomy developed from the observation ---- through regular cycles of motion.

　　(A) going to heavenly bodies

　　(B) the heavenly bodies going

　　(C) heavenly bodies that go

　　(D) that the heavenly bodies go

　　答案：D

　　解释：空格前是句子的主谓语，之后是介词短语，选项中只有D可将前后两部分连接起来，构成observation的同位语从句

　　主语从句和表语从句

　　主语从句和表语从句都是名词性从句，与宾语从句的分类、语法规则基本相同。

　　主语从句如：

　　That she has gone insane is sheer rumor.

　　Whoever says it must be a fool.

　　Whether you are innocent or not remains a question.

　　表语从句如：

　　The problem is that you have lost your way.

　　That's how we got to know the truth.

　　My major concern is whether you agree or not.

　　例题：

　　(1)

　　---- xenon could not form chemical compounds was once believed by scientists.

　　(A) For

　　(B) It was

　　(C) That

　　(D) While

　　答案：C

　　解释：空格后有两个非并列的谓语，空格处一定是需要从句引导词构成主从复合句，B可先排除，因compounds是form的宾语，不是was的主语，可见是从句作句子的主语，只有C引导的是主语从句；A、D都构成状语从句，但主句缺主语，故不对

　　(2)

　　---- has been a topic of continual geological research.

　　(A) Did the continents originate

　　(B) How did the continents originate

　　(C) Have the continents originated

　　(D) How the continents originated

　　答案：D

　　解释：空格后是句子的谓语, 空格处需要主语, A、C是倒装句无法和原句连接, how引导的主语从句不需要倒装, 所以D是正确表达

　　(3)

　　In her time, Isadora Duncan was----today a liberated woman.

　　(A) calling what we would

　　(B) who would be calling

　　(C) what we would call

　　(D) she would call it

　　答案：C

　　解释：空格前是句子的主谓语，空格处需要was的表语，A从句缺少谓语，B从句少先行词；D语义不通；C构成恰当的表语从句，符合题意