The correct answer is A. Rajmahal hills.
The Rajmahal hills are a mountain range in the Indian state of Jharkhand. They are located in the eastern part of the state, and run parallel to the Ganges River. The hills are a major source of water for the rivers of Santhal Pargana.
The other options are incorrect because they are not located in the eastern part of Jharkhand. The Ranchi plateau is located in the central part of the state, the Hazaribagh plateau is located in the north-central part of the state, and the Netarhat plateau is located in the south-eastern part of the state.
The Rajmahal hills are a popular tourist destination. The hills are home to a number of waterfalls, including the Dasam Falls, the Hundru Falls, and the Sone Falls. The hills are also home to a number of temples, including the Rajrappa Temple and the Deoghar Temple.