The correct option is D Water supply
The Harappan cities had a unique system for water supply. Water was made available to everyone equally. It is believed they were the first civilisation to achieve the great art of indoor plumbing. From each house, waste water flowed down into small drains. These small drains from houses were connected to a large underground drain that was built under the streets. From there, it was then carried out of the city. The main roads in the Indus Valley cities were as wide as our national highways, and even the ordinary streets were wide. The cities also had huge public baths. The Great Bath, which was discovered in Mohenjo-Daro was indeed a “great” Bath.