Final answer:
Amplitude modulation (A) is the correct answer in the transmission of digital data to modulate the probability that a bit has a high amplitude.
Step-by-step explanation:
The correct answer is Amplitude modulation (A).
In the transmission of digital data, the probability that a bit has a high amplitude is modulated using amplitude modulation. Amplitude modulation is a method for placing information on electromagnetic waves by modulating the amplitude of a carrier wave with an audio signal, resulting in a wave with constant frequency but varying amplitude.
In contrast, frequency modulation (B) modulates the frequency of the carrier wave, binary code (C) represents digital data as a sequence of ones and zeros, and digital signal (D) generally refers to the representation of data as discrete values.