Which of the following input operations requires conversion to a digital form before input?

The input operation that requires conversion to a digital form before input is the analog operation. Analog signals are continuous signals that represent physical phenomena, such as sound, light, temperature, and pressure, in a way that can vary infinitely. To utilize these analog signals in digital systems, such as computers, they must be converted into a digital format through a process known as analog-to-digital conversion (ADC). This conversion allows the continuous analog signals to be transformed into discrete values that the digital system can process, store, and analyze.

In contrast, digital and binary signals are already in a form that is compatible with digital systems, and discrete signals, while they may involve specific values, do not require conversion similar to analog signals. This fundamental difference underscores why analog input operations specifically necessitate conversion to a digital form for compatibility with digital technology.