When there is relative motion between RADAR and an object, the reflected signal frequency will be:

When there is relative motion between radar and an object, the Doppler effect comes into play. The Doppler effect explains how the frequency of a wave changes for an observer moving relative to the source of that wave. In the context of radar, if the object is moving towards the radar, the frequency of the reflected signal will increase, resulting in a perceived higher frequency. Conversely, if the object is moving away from the radar, the frequency of the reflected signal will decrease, leading to a perceived lower frequency.

In both cases, the reflected signal frequency will differ from the original transmitted frequency due to this relative motion, demonstrating that the frequency is altered as it reflects off the moving object. This alteration occurs whether the object is approaching or receding from the radar source, confirming that the reflected signal frequency is generally different from the transmitted frequency.

Thus, the correct answer indicates that there will always be a change in frequency as the signal reflects off an object in motion relative to the radar system.