The correct answer is: C. Both S1 & S2 are true.
A transducer is a device that converts one form of energy to another. In the context of this question, a transducer converts a physical quantity, such as temperature, pressure, or position, into an electrical signal. This electrical signal can then be used to monitor or control a process.
A sensor is a device that detects and responds to a physical stimulus or input. The sensor converts the input into a signal that can be read by an observer or by an instrument. Sensors are used in a wide variety of applications, including industrial process control, environmental monitoring, and medical diagnostics.
In conclusion, both S1 and S2 are true. A transducer is a device that converts a physical quantity into an electrical signal, and a sensor is a device that detects and responds to a physical stimulus.