The correct answer is: a) Godavari.
The Nagarjuna Sagar Dam is a gravity dam on the Godavari River in the Indian state of Telangana. It is the second largest dam in India by volume of water impounded, after the Indira Sagar Dam. The dam was constructed between 1955 and 1969 and is named after Nagarjuna, a Buddhist philosopher and teacher who lived in the 2nd century CE.
The dam has a height of 90 meters (295 feet) and a length of 1,900 meters (6,233 feet). It creates a reservoir with a capacity of 12,000 million cubic meters (423 billion cubic feet). The dam is used for irrigation, hydroelectric power generation, and flood control.
The Godavari River is the second longest river in India, after the Ganges. It originates in the Western Ghats of Maharashtra and flows through the states of Telangana, Andhra Pradesh, Chhattisgarh, and Odisha before emptying into the Bay of Bengal. The river is a major source of water for irrigation, drinking water, and hydroelectric power generation.
The other options are incorrect because they are not rivers on which the Nagarjuna Sagar Dam is built. The Krishna River is a river in India that flows through the states of Maharashtra, Telangana, Andhra Pradesh, Karnataka, and Tamil Nadu. The Tungabhadra River is a river in India that flows through the states of Karnataka and Andhra Pradesh. The Pennar River is a river in India that flows through the states of Andhra Pradesh and Tamil Nadu.