Explanation: The Very-high-frequency Omnidirectional Range (VOR) system operates by precisely measuring the phase difference between two received AC radio signals. The VOR station transmits a continuous, non-directional reference signal and a rotating, directional variable signal. Both signals are modulated with a 30 Hz component. An aircraft's receiver compares the phase of the 30 Hz component from the variable signal to the phase of the 30 Hz component from the reference signal. The phase difference between these two signals directly corresponds to the aircraft's magnetic bearing, or azimuth, from the VOR station. Therefore, option C correctly identifies that a phase difference between two AC voltages (the 30 Hz components of the VOR signals) is used to determine an aircraft’s azimuth position. Option A describes the principle of ranging, where time-of-flight determines distance (e.g., in DME or radar), not the directional principle of VOR. Option B is incorrect because VOR uses AC signals and phase, not DC voltages or peak values, for its operation. Option D correctly mentions phase difference between AC voltages but incorrectly applies it to determining *distance* from a station; VOR specifically uses phase difference for *azimuth* (bearing) information, not distance.