The correct answer is A. Rectification.
A diode is a two-terminal electronic component that allows current to flow in one direction only. It is commonly used to convert alternating current (AC) to direct current (DC). This is done by allowing current to flow through the diode in the positive half-cycle of the AC waveform, but blocking current flow in the negative half-cycle.
Amplification is the process of increasing the amplitude of a signal. This can be done using a variety of electronic components, including transistors, vacuum tubes, and op-amps. Amplification is often used in audio and video systems to increase the volume of sound or the brightness of an image.
Modulation is the process of changing one signal (the carrier signal) in accordance with another signal (the modulating signal). This can be done by varying the amplitude, frequency, or phase of the carrier signal. Modulation is often used in telecommunications to transmit information over long distances.
Filtering is the process of removing unwanted components from a signal. This can be done using a variety of electronic components, including capacitors, inductors, and resistors. Filtering is often used in audio and video systems to remove noise and interference.
In conclusion, diodes are generally used for rectification. This is because they allow current to flow in one direction only, which is necessary for converting AC to DC.