The correct answer is B. Maitreya.
Maitreya is a bodhisattva who is believed by some Buddhists to be the future Buddha. He is said to be currently living in Tushita heaven, where he is awaiting the time when he will descend to Earth to teach the dharma and liberate all beings from suffering.
Atreya is a sage who is mentioned in the Rig Veda. He is said to have been the son of Brahma and Saraswati, and he is credited with teaching the Vedas to the human race.
Nagarjuna was a Buddhist philosopher who lived in the 2nd century CE. He is considered to be one of the founders of the Madhyamaka school of Mahayana Buddhism.
Kalki is a deity who is mentioned in the Hindu scriptures. He is said to be the tenth and final avatar of Vishnu, and he is prophesied to appear at the end of the Kali Yuga to destroy evil and establish a new golden age.
In conclusion, the correct answer to the question “Who, according to the Buddhist, is believed to be the next incarnation of Gautam Buddha?” is B. Maitreya.