Bài IX:
1) => She hasn't written that dress since her sister's wedding
2) => The novel " The Adventures of Tom Sawyer " wasn't written by jack london
3) => People used to design computer new models.
4) => How long have you started working in that factory?
5) => Students aren't necessary to wear uniform today.

She hasn't written that dress since her sister's wedding

2.Jack London didn't write the novel " The Adventures of Tom Sawyer " 

The novel " The Adventures of Tom Sawyer " wasn't written by jack london

3. Computer are used to design new models. 

People used to design computer new models.