The correct answer is A. Ranchi Plateau.
The Ranchi Plateau is a plateau in the Indian state of Jharkhand. It is located in the central part of the state and is the highest plateau in Jharkhand. The plateau is drained by the Subarnarekha River and its tributaries. The climate of the plateau is tropical savanna, with a hot and humid summer and a cool and dry winter. The average annual rainfall on the plateau is about 1,000 mm.
The Chaibasa region is located in the southern part of Jharkhand. It is a hilly region with a tropical climate. The average annual rainfall in the Chaibasa region is about 1,500 mm.
The Santhal Pargana is a region in the eastern part of Jharkhand. It is a hilly region with a tropical climate. The average annual rainfall in the Santhal Pargana is about 1,800 mm.
The Panch Pargana is a region in the northern part of Jharkhand. It is a hilly region with a tropical climate. The average annual rainfall in the Panch Pargana is about 2,000 mm.
Therefore, the lowest rainfall in Jharkhand is recorded in the Ranchi Plateau.