Which of the following measures a filter’s ability to reject signals in adjacent channels?

The shape factor of a filter describes the steepness of its "skirts," which is the transition zone between the frequencies it passes (passband) and the frequencies it blocks (stopband). It is typically calculated as the ratio of the filter's bandwidth at high attenuation (like -60 dB) to its bandwidth at low attenuation (like -6 dB). A shape factor closer to 1.0 means the filter has very steep skirts and is highly effective at rejecting adjacent channel signals. Passband ripple and phase response refer to variations within the passed frequencies themselves, not the rejection of adjacent ones.