The FADEC normal control mode meters fuel to maintain a reference:

The correct answer is based on the operational principles of the Full Authority Digital Engine Control (FADEC) system in the A320 aircraft. In normal control mode, FADEC regulates fuel flow to the engines primarily to maintain a set reference for Engine Pressure Ratio (EPR).

EPR is a critical parameter that gives an indication of the engine's performance and efficiency. It is derived from the ratio of the total pressure at the engine's exhaust compared to the total pressure at the engine's inlet. By controlling fuel flow to maintain a desired EPR, FADEC ensures that the engine operates efficiently and within performance limits, optimizing thrust output.

This method of control is particularly important during takeoff and ascent, where maximum thrust is often required. It contrasts with other potential reference points like N1 (the speed of the low-pressure spool), N2 (the speed of the high-pressure spool), or RPM (which could refer to various rotational speeds but isn't a specific indicator used in this context). While these parameters are also relevant to engine operation, they do not serve as the primary reference for fuel metering in the FADEC normal control mode. Thus, the focus remains on managing EPR for effective engine performance.