The correct answer is: A. IR sensors
IR sensors are used to detect optical signals. They are a type of sensor that can detect infrared light, which is a type of light that is invisible to the human eye. IR sensors are used in a variety of applications, including security systems, remote controls, and motion detectors.
Photodiodes are a type of semiconductor device that converts light into an electrical signal. They are used in a variety of applications, including solar cells, photodetectors, and light-emitting diodes (LEDs).
Zener diodes are a type of semiconductor device that is used to regulate voltage. They are used in a variety of applications, including power supplies, voltage regulators, and surge protectors.
Transistors are a type of semiconductor device that is used to amplify and switch electronic signals. They are used in a variety of applications, including computers, cell phones, and televisions.
In conclusion, the correct answer is: A. IR sensors. IR sensors are used to detect optical signals. They are a type of sensor that can detect infrared light, which is a type of light that is invisible to the human eye. IR sensors are used in a variety of applications, including security systems, remote controls, and motion detectors.