The correct answer is (a) Brahmaputra.
The Brahmaputra is the most important river system in Arunachal Pradesh. It is the longest river in India and the ninth longest river in the world. It originates in the Himalayas and flows through the states of Arunachal Pradesh, Assam, Meghalaya, and Bangladesh. The Brahmaputra is a major source of water for irrigation, drinking water, and hydroelectric power. It is also a major transportation route.
The Ganga is the second most important river system in Arunachal Pradesh. It originates in the Himalayas and flows through the states of Uttarakhand, Uttar Pradesh, Bihar, Jharkhand, and West Bengal. The Ganga is a major source of water for irrigation, drinking water, and hydroelectric power. It is also a major transportation route and a sacred river for Hindus.
The Indus is the third most important river system in Arunachal Pradesh. It originates in the Himalayas and flows through the states of Jammu and Kashmir, Himachal Pradesh, Punjab, Haryana, and Rajasthan. The Indus is a major source of water for irrigation, drinking water, and hydroelectric power. It is also a major transportation route.
The Mahanadi is the fourth most important river system in Arunachal Pradesh. It originates in the Eastern Ghats and flows through the states of Odisha and Chhattisgarh. The Mahanadi is a major source of water for irrigation, drinking water, and hydroelectric power. It is also a major transportation route.