The correct answer is: a) Maibong.
The Dimasa Kachari Kingdom was a kingdom that existed in the Brahmaputra Valley of Assam, India, from the 13th to the 19th centuries. The kingdom was centered around the town of Maibong, which is located in the present-day Dima Hasao district of Assam. The Dimasa Kachari Kingdom was founded by the Kachari people, who are an ethnic group native to Assam. The Kachari people are believed to have migrated to Assam from the eastern Himalayas in the 12th century. The Dimasa Kachari Kingdom was a powerful kingdom that controlled a large part of the Brahmaputra Valley. The kingdom was ruled by a series of kings who were known for their military prowess and their patronage of the arts. The Dimasa Kachari Kingdom came to an end in the 19th century, when it was conquered by the British East India Company.
The other options are incorrect because they are not the centers of the Dimasa Kachari Kingdom. Option b), Dimapur, is the capital of the Nagaland state of India. Option c), Sibsagar, is a town in the Dibrugarh district of Assam. Option d), Tezpur, is a town in the Sonitpur district of Assam.