Explanation: An inverting operational amplifier circuit is characterized by a fundamental 180-degree phase shift between its input and output signals. This means that when the input voltage goes positive, the output voltage goes negative, and vice-versa, effectively "inverting" the waveform relative to the input. This direct phase opposition is a defining feature of the inverting configuration, making option C correct. Option A describes a non-inverting amplifier, where the input and output signals are in phase. Option B, a 90-degree phase shift, is typically associated with reactive components or filter circuits, not a basic inverting amplifier. Option D is incorrect because ideal voltage amplifiers, including op-amps with negative feedback, are designed for high input impedance (to avoid loading the source) and very low output impedance (to efficiently drive a load).