The main element of an analog output module is

A) AC to DC rectifier.
B) DC to AC inverter.
C) analog to digital converter.
D) digital to analog converter.

The main function of an analog output module is to convert digital signals from the PLC to analog signals that can be used by the controlled devices. This is achieved through a digital to analog converter (DAC) which converts the digital signals into analog voltage or current signals that correspond to the desired output value. Therefore, choice D is the correct answer.