1. Couldn't we make some sandwiches? (about)
What about making some sandwiches?
2. They're holding the exams in the gym. (Held)
The exams are being held in the gym.
3. Some people think another author wrote Shakespeare's plays. (by)
Some people think Shakespeare's plays were written by another author.
4. He didn't meet her because he arrived late. (If)
He would have met her if he hadn't arrived so late.
5. I really need a good night's sleep. (do)
I do need a good night's sleep.