The correct answer is option 2: a granary. Mohenjo-daro was an ancient city in the Indus Valley Civilization, and the largest building found there was indeed a granary. Granaries were important structures in ancient cities as they were used to store food and grain for the population. The granary in Mohenjo-daro was a large and well-built structure, indicating the significance of agriculture and food storage in the city. The granary would have been essential in ensuring food security for the inhabitants of the city. It is interesting to note that the Great Bath, mentioned in option 1, is another notable building in Mohenjo-daro, but it is not the largest one.