The correct answer is (b), Gond and Korku.
Gond and Korku are two of the largest tribal groups in India. They are both indigenous peoples of central India, and they have a long history of living in harmony with the natural world. Every year, they celebrate a month-long ecological important campaign festival called Van Mahotsav, during which they plant saplings of fruit-bearing trees. This festival is an important part of their culture, and it helps to protect the environment and promote sustainable development.
The other options are incorrect because they do not refer to tribal groups that celebrate Van Mahotsav. Bhutia and Lepeha are two ethnic groups from the Himalayas, Irula and Toda are two tribal groups from the southern Indian state of Tamil Nadu, and Sahariya and Agariya are two tribal groups from the central Indian state of Madhya Pradesh.