The correct answer is (a) Tharu.
The Tharu are an ethnic group native to the Terai region of Nepal and India. They are the largest scheduled tribe in Uttar Pradesh, with a population of over 4 million. The Tharu are a diverse group, with a variety of languages and cultures. They are traditionally farmers and hunters, and many still live in rural areas.
The Gond are an ethnic group native to central India. They are the second largest scheduled tribe in Uttar Pradesh, with a population of over 2 million. The Gond are a diverse group, with a variety of languages and cultures. They are traditionally farmers and herders, and many still live in rural areas.
The Khairwar are an ethnic group native to the Vindhya Range in central India. They are a small group, with a population of only around 100,000. The Khairwar are traditionally farmers and hunters, and many still live in rural areas.
The Chero are an ethnic group native to the Chhotanagpur Plateau in eastern India. They are a small group, with a population of only around 50,000. The Chero are traditionally farmers and warriors, and many still live in rural areas.