is the term used to describe when information is added to a constant frequency.

The correct answer is A. Modulation.

Explanation: Modulation is the process of varying a carrier signal’s frequency, amplitude, or phase to encode information. When information is added to a constant frequency, it modifies the signal in a way that allows it to carry data, which is essential in communication systems. Frequency itself is just a measure of how often a signal repeats, and radio wave transmission is the method used to send modulated signals. Thus, modulation specifically refers to the addition of information to a constant frequency signal.