Most people think a wetland is completely useless. No one can plant crops on it. No one can build a house on it. Therefore, engineers have drained the wetlands in order to make useful lands. Many shopping centers stand on dry land today which was once wet and marshy. Yet the soft and wet ground of a bog serves an important purpose in nature. In a marsh, the surface water can soak slowly down through the soil into the underground rock. The underground reservoir, nature's storage tank, fills slowly with that clean, filtered water which is recycled to us.

① water recycling      

② decrease of a wetland      

③ underground reservoir

④ development of dry land       

⑤ usefulness of a wetland