Answer: c. a lake
A wetland is a region where water meets the land. They form either seasonally or permanently. They include lakes, marshes, floodplains, and rice fields. The water in the wetland can be freshwater or saline water depending upon the source which is drained in the wetland. A lake is a wetland, where large body of water surrounds the land. A lake receives water from river, surface run off or from ocean. The lake may also be formed due to flood. The lake occupies the stagnated water, without drainage to other water source. Therefore, the water in lake is polluted because it is contaminated by surface run off. Hence, it does not contain freshwater.