The correct answer is A: A square wave is displayed, and the probe is adjusted until the horizontal portions of the displayed wave are as nearly flat as possible. How is compensation of an oscilloscope probe performed is that a square wave is displayed, and the probe is adjusted until the horizontal portions of the displayed wave are as nearly flat as possible. Probe compensation ensures proper frequency response. For amateur radio operators, this is important for accurate measurements. Understanding this helps when using oscilloscopes.