Choose the best answer 15. A(n) _________disease is an illness that can be passed from one person to another. A. dangerous B. chemical C. man-made D. infectious 16. A gas or other substance which is sent out into the air is _______. A. emission B. greenhouse gas C. carbon footprint D. disease 17. Air ________________ is threatening the health of older people and children. A. pollution B. acid rain C. deforestation D. global warming 18.The ozone layer helps ________________ us from the sun's rays. A. change B. reduce C. protect D. release 19. I________ two books on environment protection to complete this assignment. A. read B. have read C. have been reading D. had read 20. Many of the pictures ___________ from outer space are presently on display in the public library. A. were sent B. having sent C. sent D. sending 21. They now regret ___________ their son by providing too many material possessions. A. having spoile B. spoiled C. to have spoiled D. to have been spoiled 22. A taxi __________ us to Hoi An Ancient broke down A. taking B. was taking C. takes D. which taking