The correct answer is B. Encoder.
An encoder is a device or program that converts data from one form to another. In the context of computer science, an encoder is a program that converts data from one code system to another. For example, an encoder can be used to convert text from ASCII to Unicode, or to convert an image from JPEG to PNG.
An emulator is a program that allows one computer system to behave like another computer system. For example, an emulator can be used to run Windows programs on a Mac, or to run Android apps on a PC.
A decoder is a device or program that converts data from one form to another, in the opposite direction of an encoder. For example, a decoder can be used to convert Unicode text to ASCII, or to convert a PNG image to JPEG.
A trigger is a device or event that causes something else to happen. For example, a trigger can be used to start a program, or to take a picture.
None of these options is correct.