Explanation: Weather facsimile (WEFAX) signals transmit images by modulating an HF carrier with a range of audio tones. These tones typically span from 1500 Hz (for white) to 2300 Hz (for black), occupying an audio bandwidth of approximately 800 Hz. To properly receive this signal without distortion, the receiver's intermediate frequency (IF) filter needs a bandwidth slightly wider than the signal itself. A 1 kHz filter (C) provides sufficient bandwidth to pass the entire 800 Hz WEFAX signal, ensuring full image fidelity. At the same time, it is narrow enough to effectively reject noise and minimize interference from adjacent channels, which is crucial for clear reception on the crowded HF bands. A 500 Hz filter (A) would be too narrow, cutting off significant portions of the WEFAX signal and causing image distortion. Filters of 6 kHz (B) or 15 kHz (D) would be far too wide, allowing excessive noise and interference into the receiver, severely degrading the signal-to-noise ratio and making clear reception difficult.