Explanation: Output 3 in Figure 3D10 typically represents an integrator circuit. An integrator's output voltage is proportional to the integral of its input voltage over time. When a square wave is applied to an integrator: * During the constant positive voltage period of the square wave, the capacitor in the integrator charges linearly, causing the output voltage to rise steadily (a positive ramp). * During the constant negative voltage period, the capacitor discharges linearly in the opposite direction, causing the output voltage to fall steadily (a negative ramp). This continuous charging and discharging process transforms the square wave's abrupt transitions and flat levels into a smooth, triangular waveform. The other outputs usually depict differentiated spikes, smoothed square waves (low-pass), or the original/shifted square wave (high-pass).