c) headphones would be considered an output device.
- A keyboard is an input device, used to enter data into a computer.
- A microphone is also an input device, used to capture audio.
- A calculator can be both an input and output device, but it primarily functions as a device for calculations rather than for inputting or outputting data in the same way as computers do.
Therefore, among the options given, headphones are the correct answer as they output sound.