The correct answer is (b). A modem is a device that converts digital signals to analog signals and vice versa. It is used to connect computers to the internet, which uses analog signals.
A packet is a small unit of data that is transmitted over a network. It is used to break up large files into smaller pieces so that they can be transmitted more efficiently.
An emulator is a program that allows one computer to behave like another computer. It is used to test software that is written for a different computer.
None of these options is a device that can convert digital signals to analog signals.