Rewrite the sentence without changing the meaning

X/Rewrite the sentence without changing the meaning
1. Keeping the environment clean is very important.
- It's.
2. They will show the time machine to the public when they finish it.
- The time machine
3. He was delighted to receive his aunt's letter.
- He was delighted that
4. Old car tires are recycled to make shoes and sandals.
- People
5. I'm very sad that I wasn't accepted in that group.
- I'm very sad not
6. It's three years since I last spoke to her.
- I haven't
7. Tam doesn't type as fast as she used to.
- Tam used
8.
"Please turn down the radio for me", said my father.
- My father asked
9. Lan will be fifteen next week.
- It is Lan's
10. How long is it since you used the pen?
- When