The correct answer is (a). The Bobbili estate was a feudatory of the Golconda Sultanate, and its rulers were known for their valor. In 1757, the Bobbili estate was attacked by the British East India Company, who were trying to expand their control in the region. The Bobbili rulers fought bravely, but they were eventually defeated. The Bobbili War is remembered as one of the most heroic battles in Indian history.
The other options are incorrect. The rulers of Vizianagaram were allies of the Bobbili rulers, and they fought alongside them against the British. The Nizam of Hyderabad was a powerful ruler who was not directly involved in the Bobbili War. The Maratha Empire was a rival of the Golconda Sultanate, and it is possible that they may have supported the British in their attack on the Bobbili estate, but there is no evidence to support this claim.