There are two basic types of approach procedures:precision and non-precision. Simply stated, the non-precision approach is a standard instrument procedure that does not use an electronic glide slope. Three precision approaches use a glide slope: instrument landing sys tem (ILS), microwave landing system (MLS), and the precision approach radar (PAR). Im plementation of the MLS has stagnated as a disappointment and will be disregarded in this discussion. PAR approaches are few and far between；they will also be disregarded because the ground controller talks the pilot in. and about all the pilot can do is listen and do what the controller says. Several components are necessary for an approach to be classified as an ILS. The ground components are a localizer, glide slope, outer marker, middle marker, and approach lights. If a procedure specifies a visibility minimum based on runway visual range (RVR), it will al so need high intensity runway lights (HIRL), touchdown zone lighting (TDZL), centerline lighting (RCLS) and markings, and, naturally, the RVR transmissometers for that runway. Of course, before the pilot can accept an ILS approach, her aircraft must have the airborne equipment necessary to receive the ground components. A few variations exist. The regulations do allow a compass locator or precision radar to be substituted for the outer marker (OM) or middle marker (MM), and an airport surveil lance radar (ASR) can usually be substituted for the outer marker. All other approaches are non-precision. These primarily consist of the localizer, back course, VOR，NDB (ADF), ASR, and the newest of all, GPS approaches - although be fore long you will see both precision and non-precision GPS approaches. The VOR and NDB (ADF) approach are, in effect, designed to bring the aircraft down to, the overall airport environment, while all other approaches will bring you right down to the runway.3. Which of the following has the least developing tendency? B.