Concept:A Great Circle is formed when a plane cuts through the exact centre of the Earth, dividing it into two equal halves.Explanation:The Equator is the only line of latitude whose plane passes through the Earth's centre.Therefore, it splits the Earth into two equal hemispheres.The Tropic of Cancer, Tropic of Capricorn, and Arctic Circle are all small circles because their centres do not match the Earth's centre.Thus, among the given latitude lines, only the Equator qualifies as a Great Circle.Answer:C. Equator