The river Brahmaputra, also known as the Tsangpo-Brahmaputra, is one of the major rivers of Asia and the largest river in India by water discharge. It flows through several states and regions in India, including Arunachal Pradesh, Assam, and Meghalaya.

To answer the question directly, the correct option is "Arunachal Pradesh and Assam only."

The Brahmaputra river originates from the Angsi Glacier in the Himalayas in Tibet and enters India through Arunachal Pradesh, where it is known as the Siang river. It then flows through Assam, where it is joined by the Dibang, Lohit, and other tributaries, before continuing its journey towards Bangladesh and eventually merging with the Ganges and Meghna rivers to form the world`s largest delta.

The Brahmaputra river flows through the northeastern part of India and is a vital source of water for the region. It is known for its high water flow, which causes frequent floods in the region. The river also supports a rich and diverse ecosystem, including the famous Kaziranga National Park in Assam, which is home to the one-horned Indian rhinoceros.

In conclusion, the Brahmaputra river flows through Arunachal Pradesh and Assam only in India, before continuing its journey towards Bangladesh. The river is a vital source of water for the region and supports a diverse ecosystem.