9. Half of the people didn't appear. They were invited.
=> Half of the people who were invited  didn't appear.
10. The festival is called Easter. It is in late March or early April.
=>  The festival which is in late March or early April  is called Easter
11. The pupil gets the scholarship. He is very poor.
=> The pupil who is very poor gets the scholarship 
12. She is the nurse. She took care of me.
=> She is the nurse who took care of me.
13. My teacher punished the pupil. That pupil was naughty.
=> My teacher punished the pupil who was naughty
14. Is this the book? You want me to read it?
=>  Is this the book that you want me to read ?
15. He is the only person. He can solve this difficult problem.
=>  He is the only person who can solve this difficult problem.