A communications medium that uses single copper wire surrounded by thick insulation is:

The correct answer involves understanding the characteristics of coaxial cable. Coaxial cable comprises a single copper wire that serves as the center conductor, encased in insulation. Surrounding this insulation is a metallic shield, which acts as a ground and protects against external interference. The thick insulation is critical as it helps maintain the integrity of the signal while preventing electromagnetic interference from external sources, making coaxial cable particularly effective for transmitting data, video, and audio signals over longer distances.

In comparison, twisted-pair cables involve pairs of insulated copper wires twisted together, designed to reduce interference but not structured like coaxial cables. Optical fiber uses glass or plastic fibers to transmit data via light signals, differing significantly from copper-based transmission. Satellites, while integral to communications, are platforms in space rather than physical cabling that transmits signals via copper. This understanding clarifies why the option related to coaxial cable is the appropriate choice.