一个句子起名词的作用，在句中做主语、宾语/介词宾语、表语、同位语，那么这个句子就是名词性从句。

1.what/whatever的用法

考生应把握：what是关系代词，它起着引导从句并在从句中担当一个成分这两个作用。如：

They lost their way in the forest, and what made matters worse was that night began to fall.

(what既引导主语从句又在从句中做主语)

Water will continue to be what it is today—next in importance to oxygen.

(what既引导表语从句又在从句中做表语)

2.whoever和whomever的区别

whoever和whomever相当于anyone who，用主格与宾格取决于其在从句中做主语还是做宾语。如：

They always give the vacant seats to whoever comes first. (whoever在从句中做主语)

3.有关同位语从句的问题

(1)引导词通常为that, 但有时因名词内容的需要，也可由whether及连接副词why, when, where, how引导。that不表示任何意义，其他词表示时间、地点、原因等。如：

The problem, where I will have my college education, at home or abroad, remains untouched.

(2)同位语从句有时与先行词隔开，注意识别。如：

Evidence came up that specific speech sounds are recognized by babies as young as 6 months old.

4.whether与if在引导名词性从句时的区别

(1)主语从句只能用whether引导;

(2)whether一般多用于宾语从句的肯定式，而if引导的从句可以有否定式;

(3)whether or not可以连在一起用，而if or not则不能，or not只能放在句末;

(4)whether可以引导介词宾语从句，if则不能;

(5)宾语从句提至谓语前面时，只能用whether引导;

(6)在question, ask后面一般只用whether，question的同位语从句也用whether引导;

(7)后接不定式时，只能用whether。

5.动词believe, expect, fancy, imagine, suppose, think后的宾语从句如为否定式，一般将否定词转移到主句谓语上。