Concept:Lines of longitude are imaginary vertical lines called meridians, running from the North Pole to the South Pole.
Explanation:The Prime Meridian is the most important line of longitude because it is marked as
0∘ longitude.
All other meridians are measured east or west from the Prime Meridian.
It passes through the Royal Observatory in Greenwich, London.
It also forms the basis for the world's time zone system.
The Antarctic Circle, Arctic Circle, and Tropic of Cancer are all lines of latitude, not longitude.
Therefore, among the given options, only the Prime Meridian is a line of longitude.
Answer:C. Prime Meridian