The correct answer is: B. Sensors

A sensor is a device that detects and responds to some type of input from the physical world. Sensors are used to measure a physical quantity and convert it into a signal that can be read by an observer or by an instrument.

The input terminals of a system are the points where the system receives information from the external environment. The sensors are the devices that are used to collect this information. The sensors convert the physical quantity into a signal that can be read by the system.

The other options are incorrect because:

  • Actuators are devices that convert a signal into a physical action. They are used to control the output of a system.
  • Inputs are the signals that are received by the system from the external environment.
  • Outputs are the signals that are produced by the system and sent to the external environment.