Internal relay instructions are used when a) real-world input field devices are needed as inputs. b) real-world output field devices are needed as outputs. c) real-world field devices are not needed...

Internal relay instructions are used when a) real-world input field devices are needed as inputs. b) real-world output field devices are needed as outputs. c) real-world field devices are not needed as input or output reference instructions. d) both a and b