16._______________ means creating new products from used materials.
    A. Reduce    B. Reuse    C. Recycle    D. Rebuild
17. If the ______________  is polluted, we won’t have enough food to eat.
    A. water    B. air    C. noise    D. soil
18. We should give unused clothes to _____________to help the people in need.
    A. charity    B. factory    C. market    D. hospital
19. ___________ are you going to stay here?     ~ For a week.
    A. How often    B. How long    C. How many    D. How far
         20. ______________happens when water in lakes,rivers and oceans is polluted.
          A. Air pollution               B. Soil pollution                 C. Water pollution             D. Noise pollution