The correct answer is: a) Floating islands (phumdis).
Phumdis are unique floating islands found in Loktak Lake, Manipur, India. They are made up of organic matter, such as plant roots, and are home to a variety of plants and animals. Phumdis are an important part of the Loktak Lake ecosystem and play a role in flood control and water purification.
Coral reefs are found in tropical and subtropical waters around the world. They are made up of the skeletons of tiny coral animals called polyps. Coral reefs are home to a wide variety of marine life and are important for tourism and fisheries.
Volcanic craters are formed when volcanoes erupt. They are typically bowl-shaped depressions in the Earth’s surface. Volcanic craters can be found on land or in the ocean.
Mangrove forests are found in tropical and subtropical coastal areas. They are made up of mangrove trees, which are adapted to living in salty water. Mangrove forests are important for coastal protection and provide a habitat for a variety of marine life.