Concept:Lines joining places with equal cloud cover are known as isonephs.Explanation:Isohyets are lines that join places with equal rainfall.Isobars are lines that join places with equal atmospheric pressure.Isonephs are lines that join places with equal cloud cover.Contours are lines that join places with equal elevation or height above sea level.Since the question asks specifically about cloud cover, the correct term is isonephs.Answer:C. isonephs