Refer to figure. 
EASA learning objective 022.11.03.01.07 states: 'Explain typical position inputs to an FMS: GPS; IRS; DME; VOR; LOC; runway threshold (RWY THR).'

EASA learning objective 022.11.03.01.08 states: 'Explain how the FMS will create its own FMS position fix and that the FMS calculations will be based on the FMS position. Depending on the type of system, the FMS position may be calculated from: a single source of position data where the most accurate data available at a given time will be used; multiple sources from which a position will be derived using the combined inputs.'

One of the functions of a flight management system (FMS) is to calculate an aircrafts present position accurately. To do this it takes inputs from a selection of navigation devices fitted to the aircraft:

• Global Navigation Satellite System (GNSS) - GPS is currently the most widely used GNSS system and provides very accurate postion data but it can be jammed or spoofed.
• Inertial Systems (INS/IRS) - 2 or 3 INS/IRS are normally fitted to medium/long haul aircraft, their accuracy drifts over time.
• Radio Navigation Aids - VOR, DME and ILS localiser (LOC) can be automatically used by the FMS for position fixing. NDB's are not used as they're too innacurate
• Runway Threshold Update - when power is applied on take-off the FMS can update its position based on the known position of the runway threshold.

In practice, if the aircraft has a working GPS system the FMS position will be based on the GPS source, in the absence of an accurate GPS input the FMS will use a 'mix' position based on a combination of IRS and radio inputs. The present position that the flight management computer (FMC) is using, and it's source, can be checked on the FMS CDU 'Position Monitor' page (see figure).

Note: You may see several variations of this question but the correct answer will always include a combination of GPS; IRS/INS; DME; VOR; LOC or RWY THR. It will not include NDB, or ILS Glideslope (G/S).