People used to think that wetlands were wasted land. Developers would drain them with ditches ,fill them in with tons of soil,and build houses,schools,and parking areas on them.Then scientists began to realize the important role wetlands played in the environment. Wetlands act like giant sponges  during storms.They soak up extra storm water and afterward release it slowly back into the water cycle.This helps prevent flooding. Towns where people have drained wetlands have found that in a big storm,their streets and homes are often flooded because there are no wetlands to soak up the excess water. Wetlands also act as giant filters where pollutants are absorbed and dissolved over time.Though wetlands can become polluted from dumping,wastewater,and fertilizer runoff from farm fields,they are able to process some pollutants over time because of all the microorganisms and plants living there. Wetlands are especially important for providing homes and breeding grounds to millions of birds,fish,and amphibians worldwide. Many wetlands have become national wildlife refuges ,where you can go to take pictures and look at birds and animals. The Everglades are a huge wetland that once covered more than four million acres of southern Florida. Sometimes called the "river of grass",the Everglades are a shallow sheet of water that slowly flowed across a grassy plain. In the late 1800s people began draining parts of the Everglades for development. Roads were built and towns sprang up.The Everglades shrank to half its original size. Cities like Miami grew up where once there was a thriving wetland. Sewage and waste from the cities were pumped into the remaining wetlands. Over time scientists began to see the importance of the Everglades. Even with its smaller size,the Everglades filtered the pollutants coming from the cities,absorbing the worst of it like a sewage treatment plant. During storms the Everglades protected the cities from storm surge flooding. They also are just a great place to visit and see wildlife. We can infer from the passage that  _  .
some wetlands can be used to build cities or towns wetlands in the world are disappearing fast wetlands play an important role in the ecosystem wetlands are especially important to wildlife