The correct answer is: a) Kamarupa Kingdom.
The Kamarupa Kingdom was a major power in the region of Assam from the 3rd to the 13th centuries. It was during this time that Hinduism and Sanskrit culture were first introduced to the region. The Kamarupa kings were patrons of the arts and sciences, and they built many temples and monasteries. They also encouraged the study of Sanskrit literature and philosophy. As a result of their efforts, Hinduism and Sanskrit culture became firmly established in Assam.
The other options are incorrect for the following reasons:
- Option b) Invasion of the Ahoms: The Ahoms were a Mongoloid people who invaded Assam in the 13th century. They were not responsible for the spread of Hinduism and Sanskrit culture in the region.
- Option c) Influence of Southeast Asia: Southeast Asia was a major center of Hindu and Buddhist culture, but there is no evidence that it had a significant influence on the spread of these religions in Assam.
- Option d) Arrival of Jain monks: Jainism is a minority religion in Assam, and there is no evidence that Jain monks played a significant role in the spread of Hinduism and Sanskrit culture in the region.