Don't lose your passport, as I did last year.

She was frightened than I was.

You are tired as I am.

以上三句均有错误，修改如下：

Don't lose your passport as I did last year. 应该去掉逗号，因为not的否定范围涵盖as从句。

She was more frightened than I was. 漏掉了more。

You are tired, as I am. 应该加逗号。

试比较：You are tall, as I am. 你个子高，我也个子高。（二人都是高个子）

这不同于 You are as tall as I am. 你和我一样高。（二人可能都是高个子，都是矮子，或者都是中等个头。只是比较二人的相对高度。）

通常认为as和than引导比较分句时是从属连词，在从句中不作成分，那么比较分句中就必须省略一个成分。网友可以从以下分析体会从句省略的成分：

Don't lose your passport, as I did last year.

Don't lose your passport. I did so last year. 改为比较分句后，必须省略so.

She was more frightened than I was.

I was frightened. She was more frightened. 改为than比较分句后，frightened必须省略。

You are tired， as I am.

I am tired. You are tired, too. 改为as比较分句后，tired必须省略。

比较分句必须省略一个成分，是因为than和as的使用。所以从另一个角度，我们可以说than和as其实并不是连词，而是比较代词或比较副词，在引导比较分句的时候，还要在分句中作成分，这样，比较分句结构就是完整的，没有省略，而是than和as作为比较对应项在从句中作了成分。按照这种观点，可以对以上三句重新分析如下：

Don't lose your passport as I did last year.as在从句中作状语

She was more frightened than I was. than在从句中作表语

You are tired， as I am. as在从句中作表语

以上二种分析方法，网友可以根据自己的理解选择一种。