The correct answer is (a). Andaman and Nicobar Islands are a group of islands in the Bay of Bengal. They are home to a wide variety of plants and animals, many of which are found nowhere else in the world. The islands are also home to a number of indigenous peoples, who have lived there for thousands of years.
The Gangetic Plain is a vast plain in northern India. It is home to a large number of people, and is also an important agricultural region. However, the Gangetic Plain is not a biodiversity hotspot.
Central India is a region in the middle of India. It is home to a variety of plants and animals, but it is not as biodiverse as the Andaman and Nicobar Islands.
Therefore, the correct answer is (a).