Using source 2, what aspect of the ruins is most unique to the indus river valley civilization? a the ruins were built on top of a hill, signifying that rulers had greater social status than the rest of the population they ruled over. b the fields beyond the ruins were used for farmland, because people living in cities had no room to grow crops, which meant others had to grow food for them. c the ruins show evidence of an organized drainage and sewer system designed to carry away waste and keep the city clean. d the ruins are one of many sites on the banks of an ancient river, which meant that they were connected by a waterway that made trade between cities easy.