Hint: The Battle of Buxar ended in 1764. This marked the signing of the Treaty of Allahabad in 1765. This treaty marked the beginning of the British rule and their political and constitutional involvement in India.
Complete answer: After the Battle of Buxar, The British obtained the Diwani rights from the Mughal Emperor Shah Alam II who was the son of late AlamgirII. Robert Clive signed the Treaty on behalf of the East India Company. Allowing the Diwani Rights to the East India Company meant that they would be able to collect taxes on behalf of the Emperor in the eastern region which was Bengal-Bihar and Orissa. A sum of 26 lakh rupees was paid by the Company in order to secure its rights. This money was to be used for the maintenance of the Emperor’s court in Allahabad. The region of Awadh was returned to Shuja -ud-Daul, However Allahabad and Kora was taken away from him. Shuja-ud-Daula had to pay a sum of Fifty lakh rupees to the British as war insurance.
Option C is the correct answer.
Note: Nawab Shuja-ud-Daula entered into an alliance with the British in which the British would give him protection but the Nawab had to pay for the troops. The Treaty of Allahabad gave the British around 40,000 square kilometres of fertile land from which the British could generate taxes.