Explanation: In RADAR systems, the "modulation frequency" often refers to the Pulse Repetition Frequency (PRF), which is the rate at which radar pulses are transmitted. The PRF is crucial for determining the radar's maximum unambiguous range. A lower PRF allows more time for a pulse to travel to a distant target and return as an echo before the next pulse is transmitted, preventing range ambiguity. For many common radar applications, such as air traffic control, weather monitoring, or general surveillance, detecting targets at significant distances is important. This necessitates a relatively low PRF, typically ranging from tens to a few hundred Hertz. The 60 to 500 Hz range aligns well with these practical requirements, enabling long unambiguous ranges. Higher modulation frequencies (options B, C, and D) would result in a much shorter listening time between pulses. This severely limits the maximum unambiguous range the radar can detect, making these frequencies unsuitable for most general-purpose radar applications.