The correct answer is D. All of the above.
An operational amplifier (op-amp) is a high-gain electronic amplifier with a differential input and a single-ended output. It is a versatile device that can be used to perform a variety of mathematical operations, such as addition, subtraction, multiplication, and division. Op-amps are also used in feedback circuits, which can be used to control the gain, frequency response, and other characteristics of an amplifier.
Op-amps can be used to subtract two or more signals by connecting the inputs of the op-amp to the two signals to be subtracted. The output of the op-amp will be the difference between the two input signals.
Op-amps can also be used to sum two or more signals by connecting the inputs of the op-amp to the two signals to be summed. The output of the op-amp will be the sum of the two input signals.
Op-amps use the principle of feedback to control their gain, frequency response, and other characteristics. Feedback is a technique in which a portion of the output signal of an amplifier is fed back to the input of the amplifier. This feedback can be used to stabilize the amplifier, reduce noise, and improve its performance.
In conclusion, an operational amplifier can be used to subtract two or more signals, sum two or more signals, and uses the principle of feedback.