What kind of transmission line has a centre wire inside an insulating material that is covered by a metal shield or sleeve?

A coaxial cable gets its name because its two conductors share the same central axis. It is constructed with a single center wire (inner conductor) surrounded by a layer of insulating material (the dielectric), which is in turn completely enclosed by a braided or solid metallic shield (outer conductor). This design keeps the electromagnetic field confined entirely within the space between the inner and outer conductors, preventing the signal from radiating outward and shielding it from outside interference. This makes coaxial cable highly practical and popular for amateur radio station wiring. The other options describe completely different geometries. Open-wire and window lines consist of two parallel wires separated by air or plastic cutouts, while a waveguide is a hollow metal tube with no center conductor at all.