Which of the following is a type of analog-to-digital conversion?

Successive approximation is a very common architecture used in analog-to-digital converters (ADCs). It works by using an internal digital-to-analog converter and a comparator to perform a binary search on the input signal. The circuit compares the incoming analog voltage to a reference voltage, cutting the possible voltage range in half with each successive step. This rapidly narrows down the precise digital value representing the analog signal's amplitude. The other options listed are entirely different concepts. Level shifting merely changes a signal's DC offset, phase reversal inverts a signal, and harmonic regeneration is unrelated to digitizing continuous analog signals.