EX2:
1. The word is on the tip of my tongue.
2. They rent the security guards to discourage the people who try to steal money.
3. 15 million people in the world had been affected by aids by 1997.
4. Destroying the rainforests will destroy the environment.
EX3:
1. She has lived in that house since 1989.
2. If you don't have an injection, you will get cholera.