The correct answer is: b) The indigenous inhabitants of Sikkim.
The Lepcha are an ethnic group indigenous to the eastern Himalayas, primarily in Sikkim, India. They are believed to be the earliest inhabitants of Sikkim, and their language, Lepcha, is one of the oldest languages in the region. The Lepcha are a matrilineal society, and their traditional religion is a form of animism.
Option a) is incorrect because the Lepcha are not recent migrants to Sikkim. They have been living in the region for centuries, and are considered to be the indigenous inhabitants of Sikkim.
Option c) is incorrect because the Lepcha are not a primarily nomadic tribe. They are a settled people, and have been living in the same villages for generations.
Option d) is incorrect because the Lepcha are not a Hindu religious sect. They have their own traditional religion, which is a form of animism.