语法填空
①Is there anything ___________ I can do for you?
②The speaker will tell us about some writers and their works ___________are known to us.
③On the train I saw a student ___________ I thought was your sister.
④This is the very letter ___________ I am looking for.
⑤Edison built up a factory ___________ produced things that had never been seen before.
⑥I am going to meet Tom ___________ they say is a good boy.
⑦The books on the desk, ___________ covers are shiny, are prizes for us.