下列句子中均有一处错误,请指出来.（不知怎么改,）

下列句子中均有一处错误,请指出来.（不知怎么改,）
1.National Day is coming.We will have a seven-day holiday.
2.Edison's father asked him why he wanted a science lab for .
3.She hasn't got a chair to sit.
4.Xiao li has left for about three weeks.
5.Ann was seen go into the teacher's office just now.
6.That's easy for a child to oen her eyes.