The correct answer is: A. Requires a change to an analog signal.
When computers communicate using standard telephone service, the digital signals from the computer are converted to analog signals that can be transmitted over the telephone network. This is because the telephone network is designed to transmit analog signals, not digital signals.
The conversion from digital to analog signals is done by a device called a modem. The modem converts the digital signals into a series of electrical pulses that can be transmitted over the telephone network. The pulses are then converted back into digital signals at the receiving end.
The conversion from digital to analog signals and back again introduces some noise and distortion into the signal. This is why communication between computers using standard telephone service is not as efficient as communication using other methods, such as a dedicated network connection.
However, standard telephone service is a relatively inexpensive way to connect computers, and it is widely available. This makes it a good option for many businesses and individuals.
Options B, C, and D are incorrect because they do not accurately describe communication between computers using standard telephone service.
Option B states that communication between computers using standard telephone service is most efficient. This is not true. Communication between computers using standard telephone service is not as efficient as communication using other methods, such as a dedicated network connection.
Option C states that communication between computers using standard telephone service produces little noise and few disturbances. This is also not true. The conversion from digital to analog signals and back again introduces some noise and distortion into the signal.
Option D states that all of the above are true. This is also not true. Only option A is true.