Q. Which of the following is a voiceband channel ?

Explanation by: Mr. Dubey

A voiceband channel is a communication channel with a bandwidth range of approximately 300 Hz to 3400 Hz, which is suitable for transmitting voice signals.
(A) Telephone line: Yes, this is typically designed to carry voice frequencies in the voiceband range. So it's a voiceband channel.
(B) Coaxial cable: No, it supports much higher frequencies and wider bandwidths (used for broadband).
(C) Microwave systems: No, they operate at very high frequencies, far beyond voiceband.
(D) Telegraph line: No, it's a narrowband channel, not specifically designed for voice transmission.
So, Telephone line is the correct voiceband channel.