The correct answer is: A. PLC
A PLC (programmable logic controller) is a digital computer used for automation of industrial processes, such as in manufacturing, oil and gas, water and wastewater treatment, etc. PLCs are used to control and monitor a variety of devices, such as motors, valves, sensors, and alarms.
A HMI (human-machine interface) is a computer-based system that allows operators to interact with a PLC. HMIs typically provide a graphical user interface (GUI) that allows operators to view process data, send commands to the PLC, and receive alarms.
An alarm task is a software program that monitors the PLC for alarms. When an alarm occurs, the alarm task will notify the operator and take appropriate action, such as shutting down the process.
An I/O task is a software program that manages the input and output (I/O) of the PLC. The I/O task is responsible for reading data from sensors and sending commands to actuators.
The PLC is the heart of a SCADA system because it is responsible for controlling and monitoring the process. The HMI, alarm task, and I/O task are all important components of a SCADA system, but they are not as critical as the PLC.