The correct answer is (a) Godavari river.
Nagarjuna Sagar is a reservoir on the Godavari River in the Indian state of Telangana. It is the largest reservoir in India by capacity and the second largest by surface area. The dam was constructed between 1955 and 1963 and is named after Nagarjuna, a Buddhist philosopher and teacher who lived in the 2nd century CE.
The reservoir is used for irrigation, drinking water supply, hydroelectric power generation, and flood control. It is also a popular tourist destination.
The other options are incorrect because:
(b) The Krishna River is a river in India that flows through the states of Maharashtra, Karnataka, Andhra Pradesh, and Telangana. It is the second longest river in India after the Ganges.
(c) The Penganga River is a river in India that flows through the states of Maharashtra and Telangana. It is a tributary of the Godavari River.
(d) The Tungabhadra River is a river in India that flows through the states of Karnataka and Andhra Pradesh. It is a tributary of the Krishna River.