修改病句：找出下列句子的错误
1、We don't know that we can do about it.
2、The old man said he had joined the army in 1965.
3、could you tell me how I could get to the nearest post office .
4、Mary said she did not heard from her old classmates since September .
5、Charls asked he could use my car .
6、Mom asked me where I will go the next day .
7、Don't look at someone else poper ,John ,You should do it by yourself .
8、The teacher gave a series of example in her lecture in order that everybody could understand.