The correct answer is D. R-Marker.
A repeating signal is a type of signal that is transmitted multiple times, usually with a short delay between each transmission. This is done to improve the reliability of the signal, as it is less likely that all of the transmissions will be lost or corrupted.
The R-Marker is a special type of marker that is used to indicate the start and end of a repeating signal. It is typically inserted at the beginning of each transmission, and it is also inserted at the end of the last transmission in a sequence. This allows the receiver to determine where the individual transmissions begin and end, and it also helps to prevent the receiver from losing track of the signal.
The other options are not available in repeating signals. G-Marker, C-Marker, and P-Marker are all types of markers that are used in non-repeating signals. They are not necessary for repeating signals, as the R-Marker provides all of the necessary information.
Here is a diagram that illustrates the use of the R-Marker in a repeating signal:
[Diagram of a repeating signal with the R-Marker inserted at the beginning and end of each transmission]
As you can see, the R-Marker is inserted at the beginning of each transmission, and it is also inserted at the end of the last transmission in a sequence. This allows the receiver to determine where the individual transmissions begin and end, and it also helps to prevent the receiver from losing track of the signal.