网友需要明确一个概念：同位语是名词性结构。介词短语是不能作同位语的。同位语和它所修饰的名词在意义上是同一的，即二者说的是一回事，只不过换了一个说法而已。例如：I went back to my hometown Beijing. I went back to Beijing, my hometown. 这二个句子中，Beijing和my hometown 互为同位关系，我们说后面的名词是前面名词的同位语。

名词和其同位语之间的关系可以表示为一个名词作表语的句子。

Beijing is my hometown.

My hometown is Beijing.

有时同位关系可以通过介词短语表示，例如 I live in the city of Beijing. 逻辑上北京就是那个城市，是同位关系，但语法上Beijing是介词of的宾语，构成of Beijing这个介词短语。介词短语是不能作同位语的，所以of Beijing是 the city的定语，而不是同位语，但是语义上，介词of表示同位关系。即 of的宾语说明 the city 具体是哪个城市。所以网友应该知道of 介词短语作后置定语，表示同位关系这种语法分析。

同位语也可以由that从句、wh-从句等其他名词性结构充当。例如：

the fact that one plus one is two

the question who did this

the problem what we should do with so much pollution

以上三句中that从句、who从句和what从句都是前面名词的同位语。我们可以看出名词和同位语之间存在主系表关系：

The fact is that one plus one is two.

The question is who did this.

The problem is what we should do with so much pollution.

wh-从句作同位语通常是前面省略了介词 of 的结果。即：

the question who did that = the question of who did this

the problem what we should do with so much pollution = the problem of what we should...

当wh-从句前有介词of时，语法分析为of 介词短语作名词的后置定语，wh-从句与名词为同位关系。如果wh-从句直接位于名词后，则分析为wh-从句作同位语。

What's the problem with the computer?
You should have no problem with reading this language.

这二个句子中的with意为“关于、涉及”，with后的名词与problem并不是同位关系，介词with也没有表示同位关系的功能。所以这二个句子中的with介词短语都是定语，与同位语无关（无论从语义上，还是从语法上）。