Final answer:
Notch filters (option A) provide filtering on sub-split return frequencies by blocking or attenuating specific frequencies. High-pass and low-pass filters allow frequencies above or below a certain threshold, respectively. Inductors in circuits act as low-frequency filters.
Step-by-step explanation:
When filtering on sub-split return frequencies, the correct mitigation device to use is notch filters (A). A notch filter is designed to block or attenuate a specific range of frequencies, allowing all others to pass. This is especially useful in scenarios where specific unwanted frequencies need to be eliminated or reduced.
By contrast, high-pass filters (B) allow frequencies above a certain threshold to pass, blocking lower frequencies. Low-pass filters (C) do the opposite, allowing only frequencies below a certain threshold to pass and blocking higher frequencies. Band-pass filters (D) allow frequencies within a certain range to pass and block frequencies outside of that range.
If capacitors in a circuit are replaced by inductors, the behavior of the circuit changes. An inductor in a circuit typically acts as a low-frequency filter, allowing low frequencies to pass while impeding higher frequencies. Consequently, replacing capacitors with inductors would result in the creation of high-frequency filters.