The correct answer is: c) Migrants from neighboring Nepal.
Nepali is an Indo-Aryan language spoken by about 29 million people, primarily in Nepal, where it is the official language. It is also spoken in India, Bhutan, and Bangladesh. Nepali is a member of the Eastern Pahari group of languages, which also includes Maithili, Bhojpuri, and Magahi.
The original inhabitants of Sikkim are the Lepchas, who speak a Tibeto-Burman language. The descendants of Tibetan settlers in Sikkim speak Tibetan. The former ruling dynasty of Sikkim was the Namgyal dynasty, which spoke Tibetan.
Migrants from neighboring Nepal began to settle in Sikkim in the 18th century. They brought with them the Nepali language, which gradually became the lingua franca of Sikkim. In 1975, Sikkim became an Indian state, and Nepali became one of the official languages of India.
Today, Nepali is the most widely spoken language in Sikkim. It is used in government, education, and the media. It is also the language of the majority of the population.