13. Nhi enjoyed chatting on the phone with her friends.
14. Nam will not be able to go to the cinema at 3.30 p.m. this Monday because he is having a class then.
15. He hopes that Mary will come to the party tonight.
16. Noise pollution in big cities can lead to hearing problems.
17. Lots of aquatic animals die because of oil spills.
18. If you were the president of the country, what would you do to protect the environment?
19. One way to save the environment is to use renewable energy sources.
20. This boy suffers from birth defects because his parents were exposed to radioactive pollution.