The correct answer is D. Gaya.
The Phalgu river is a tributary of the Son River in the Indian state of Bihar. It originates in the Kaimur Range and flows through the districts of Gaya, Nalanda, and Patna. The river is sacred to Hindus and is a popular pilgrimage destination.
The Phalgu river is mentioned in the Mahabharata and the Ramayana. In the Mahabharata, the river is said to have been the site of the Kurukshetra War. In the Ramayana, the river is said to have been the site of the battle between Rama and Ravana.
The Phalgu river is a major source of irrigation for the districts of Gaya, Nalanda, and Patna. The river is also a popular destination for fishing and boating.
The Phalgu river is a beautiful and important river in Bihar. It is a source of water, irrigation, and recreation for millions of people.
Option A is incorrect because Rohtas is a district in Bihar, but the Phalgu river does not flow through it.
Option B is incorrect because Arwal is a district in Bihar, but the Phalgu river does not flow through it.
Option C is incorrect because Aurangabad is a district in Bihar, but the Phalgu river does not flow through it.