Which of the following can be used to replace an inoperative OM or MM?

The use of a compass locator and DME (Distance Measuring Equipment) as a replacement for an inoperative OM (Outer Marker) or MM (Middle Marker) is the correct choice due to their ability to provide essential navigation information that is critical for instrument approaches.

A compass locator signifies the location of the final approach fix and operates similarly to a non-directional beacon (NDB), while DME offers accurate distance information from the station. Together, they help pilots determine their position relative to the approach path, which is crucial when utilizing instrument approaches, especially during low visibility conditions.

While precision radar could theoretically aid in navigation, it is not a conventional practice for replacing marker functions directly in approaches. VORs, although useful for navigation, do not provide the same localized guidance needed that markers do during the critical phases of an approach. Adverse weather radar, while vital for situational awareness regarding weather conditions, does not serve a navigational function that would directly replace the need for an OM or MM.

Thus, the combination of a compass locator and DME effectively maintains the necessary guidance for pilots during an instrument approach when the traditional markers are inoperative.