Option a is the correct answer. Colonel Colin Mackenzie, a British army officer and surveyor, played a crucial role in the discovery and documentation of the ruins of the Vijayanagara Empire at Hampi. He was appointed as the first Surveyor General of India by the British East India Company. In 1800, he came across the ruins of Hampi, the capital city of the Vijayanagara Empire, which had been abandoned and lost to history.