Explanation: A SINAD (Signal-plus-Noise-plus-Distortion to Noise-plus-Distortion) meter is designed to quantify receiver sensitivity and audio quality. Measurements of signal-to-noise or signal-to-distortion ratios are conventionally expressed in decibels (dB), making the dB scale appropriate for a SINAD meter. The defining characteristic for a SINAD measurement is the precise removal of the original test tone from the receiver's audio output. Typically, a 1000 Hz audio tone modulates the RF signal used for testing. To isolate the Noise-plus-Distortion components, this 1000 Hz tone must be sharply filtered out. A sharp 1000 Hz bandstop (or notch) filter achieves this, allowing the meter to measure only the remaining noise and distortion. Options B, C, and D are incorrect because a bandpass, highpass, or lowpass filter would not specifically and effectively remove only the 1000 Hz test tone while accurately capturing the broader spectrum of noise and distortion components, which is essential for a proper SINAD calculation.