Option a is the correct answer Great Bath, ancient structure at Mohenjo-daro, Pakistan, an archaeological site featuring ruins of the Indus civilization. The Great Bath dates to the 3rd millennium BCE and is believed to have been used for ritual bathing. The Great Bath was a large rectangular tank in a courtyard surrounded by a corridor on all four sides. There were two flights of steps on the north and south leading into the tank, which was made watertight by setting burnt bricks on edge and using a mortar of gypsum. There were rooms on three sides, in one of which was a large well. Water from the tank flowed into a huge drain. Across a lane to the north lay a smaller building with eight bathrooms, four on each side of a corridor, with drains from each bathroom connecting to a drain that ran along the corridor. The uniqueness of the structure is that it is located at the Citadel, this has led scholars to suggest that it was meant for some kind of a special ritual bath.