Final answer:
A good example of a message signal is a baseband signal, which is the original form of information like audio or video, before being modulated onto a carrier wave for transmission.
Step-by-step explanation:
A good example of a message signal is (c) A baseband signal. A message signal is information in its original form, like an audio or video signal, before being transmitted over a distance. Baseband signals are typically at lower frequencies and contain the information that needs to be communicated. They are then modulated onto a higher frequency signal, known as the carrier, for transmission. In contrast, (a) A radio frequency signal typically refers to the carrier signal alone, without any message imposed on it. A pilot carrier (b) is a reference signal used in various communication systems, and Aₘδ(t) (d) and AₘΠ(t/T) (e) are mathematical representations of signals which do not reflect the original message by themselves.
For example, in AM (amplitude modulation) and FM (frequency modulation) transmission used in radio broadcasting, baseband signals (audio) modulate the carrier wave. The carrier wave in AM transmission has its amplitude altered in proportion to the baseband signal, while in FM transmission, it is the frequency that is modulated.