1) 1. at
2. by
3. with
4. off
5. in
2) 1. I have answered five e-mails so far.
2. She has been working since seven o’clock
3. Sandy and her mum are baking a cake at the moment
4. Let's ask Tom. He will probably know the answer.
5. They will probably be watching TV right now.
6. She is well-informed about politics because she reads the newspaper every day