V. Each sentence below contains a mistake. Write the mistake and correct it.
1. This cooker, which my sister bought it yesterday, is very expensive. …………….
2. I haven’t finished to decorate the Christmas tree yet. …………….
3. The gas from the chemical factory is extreme harmful to our health. ……………..
4. My son didn’t worn that uniform since last year. …………….
it=>x
to decorate => decorating
extreme=>extremely
didn't worn => hasn't worn