In which of the following circumstances should a technician ensure that he or she is grounded to minimize ESD?

In which of the following circumstances should a technician ensure that he or she is grounded to minimize ESD?
A . The technician is conducting a current test on a device.
B . The technician is working on a device that is plugged in to AC power.
C . The technician is cleaning the display on a device after reassembly.
D . The technician is replacing a circuit board inside a device.

Answer: D