WORLD CIVILIZATION

Detailed explanation-1: -In fact, “cataract” means both an opacity of the lens and a torrent of water and is derived from the Greek word kataráktēs meaning the fall of water. A wall painting in an ancient tomb at Thebes (about 1200 B.C.) seems to reveal the treatment of an eye by an oculist.

Detailed explanation-2: -A cataract is a shallow stretch of turbulent waters formed where flowing waters encounter resistant rock layers. In the case of the Nile cataracts, large outcroppings of granite make the flow of the river unpredictable and much more difficult to traverse by boat.