The correct answer is: a) River Dolphins.
The Vikramshila Gangetic Dolphin Sanctuary is a protected area in the Indian state of Bihar. It was established in 1991 to protect the endangered Ganges river dolphin. The sanctuary covers an area of 1,000 square kilometers and includes the river stretch between Bhagalpur and Kahalgaon.
The Ganges river dolphin is a freshwater dolphin that is found in the Ganges, Brahmaputra, and Meghna river systems. It is one of the most endangered dolphins in the world, with a population of only about 2,000 individuals. The main threats to the Ganges river dolphin are habitat loss, pollution, and overfishing.
The Vikramshila Gangetic Dolphin Sanctuary is one of the most important conservation areas for the Ganges river dolphin. The sanctuary provides a safe haven for the dolphins and helps to protect them from the threats they face. The sanctuary also conducts research on the dolphins and educates the public about their conservation.
The other options are incorrect because they are not the focus of the Vikramshila Gangetic Dolphin Sanctuary. Elephants, tigers, and rhinoceros are all found in India, but they are not the focus of this particular sanctuary.