Final answer:
The most widely used networking medium for modern Ethernet LANs is twisted pair cable. Coaxial cable and fiber-optics are also used in networking, but to a lesser extent. Infrared is not commonly used.
Step-by-step explanation:
The most widely used networking medium for modern Ethernet LANs is a. twisted pair cable. Twisted pair cable consists of pairs of insulated copper wires twisted together, which helps to reduce electromagnetic interference. It is commonly used for Ethernet connections in homes, offices, and data centers.
Coaxial cable (b. coaxial cable) was used extensively in the past, but it has been largely replaced by twisted pair cable for Ethernet LANs.
Fiber-optics (c. fiber-optics) is another type of networking medium that uses thin strands of glass or plastic to transmit signals as pulses of light. It is used for high-speed and long-distance connections, such as in telecommunications networks.
Infrared (d. infrared) is not commonly used as a networking medium for Ethernet LANs. It is primarily used for wireless communication, such as remote controls and wireless data transfer between devices.