The correct answer is: a) Assamese.
Assamese is an Indo-Aryan language spoken by the Assamese people of Assam, India. It is the official language of Assam and is also spoken in parts of Arunachal Pradesh, Nagaland, Meghalaya, and Tripura. Assamese is written in the Assamese script, which is derived from the Brahmi script.
Bengali is an Indo-Aryan language spoken by the Bengali people of Bangladesh and West Bengal, India. It is the official language of Bangladesh and is also spoken in parts of Assam, Meghalaya, Tripura, and Arunachal Pradesh. Bengali is written in the Bengali script, which is derived from the Brahmi script.
Hindi is an Indo-Aryan language spoken by the Hindi people of India. It is the official language of India and is also spoken in parts of Nepal, Pakistan, and Bangladesh. Hindi is written in the Devanagari script.
Bodo is an Austroasiatic language spoken by the Bodo people of Assam, India. It is the official language of Bodoland Territorial Region, India. Bodo is written in the Bodo script, which is derived from the Brahmi script.
Assamese is the primary language spoken in Assam because it is the native language of the majority of the population of Assam. Bengali is the second most spoken language in Assam because it is the native language of a significant minority of the population of Assam. Hindi is the third most spoken language in Assam because it is the native language of a small minority of the population of Assam. Bodo is the fourth most spoken language in Assam because it is the native language of a very small minority of the population of Assam.