Explanation: A center-tap connection in a filament supply transformer establishes a reference point, often connected to ground or the cathode reference potential. This design creates a balanced AC voltage across the filament relative to this reference. Option B explains the core mechanism: with the center-tap as a reference, the AC voltage on one side of the filament is positive while the other side is equally negative. This symmetry means that any AC influence on the tube's operation, such as the potential difference between the control grid and the effective cathode, is largely cancelled out. Option A describes the crucial benefit of this cancellation: by minimizing the AC voltage difference relative to the control grid or other signal paths, it prevents the filament supply's hum voltages from modulating the desired signal passing through the tube, ensuring a clean output. Both aspects are correct and describe why a center-tap is essential for reducing hum in vacuum tube circuits.