The correct answer is: C. Rajmahal
In 1763, Major Adams gained rule over the Rajmahal district of Jharkhand. This was part of the British East India Company’s expansion into the Indian subcontinent. The Rajmahal district was a strategically important area, as it controlled the trade routes between Bengal and Bihar. The British were able to establish control over the district through a combination of military force and diplomacy.
The other options are incorrect. Giridih and Santhal Pargana are both districts in Jharkhand, but they were not under British rule in 1763. None of the above is also incorrect, as Major Adams did gain rule over a specific area of Jharkhand in 1763.