An example of a lotic ecosystem is:

1. A

   Swamps

   Swamps claim standing or slow-moving water bodies with emergent vegetation. This option represents a lentic or palustrine system rather than a flowing water lotic system.

2. B

   Ponds

   Ponds claim shallow, standing freshwater habitats where water does not flow continuously. This option describes a classic lentic ecosystem instead of the requested lotic environment.

3. C

   Rivers

   Rivers claim flowing water systems characterized by unidirectional movement from source to mouth. This option is the official key because running water ecosystems are scientifically classified as lotic environments.

4. D

   Marshy area

   Marshy area claims saturated, wetland environments dominated by herbaceous plants. This option refers to a lentic or wetland system rather than a moving water lotic ecosystem.

Summary. Official key is (c) Rivers. Lotic ecosystems specifically refer to freshwater bodies with flowing water, such as rivers, streams, and creeks. In contrast, swamps, ponds, and marshy areas are classified as lentic ecosystems characterized by standing or still water. Understanding this fundamental ecological distinction is essential for environmental geography questions in the UPPSC Prelims. Therefore, only option (c) correctly identifies an example of a lotic ecosystem.