PLC emergency stop circuits should be:

A) hardwired outside the controller program.
B) programmed as part of the MCR instruction.
C) programmed as part of the zone control last state instruction.
D) programmed as an immediate input instruction.

Emergency stop circuits should always be hardwired outside the controller program to ensure that they are directly and immediately accessible to an operator in case of an emergency. This is a safety measure to prevent delay or failure of the emergency stop function due to issues within the program or controller.