A touch screen is the only device which works as both an input and an output device among the given options. You view the options available to you on the screen (output) and you then use your finger to touch the option that you have chosen (input).
A computer system consists of two major elements: hardware and software. Computer hardware is the collection of all the parts you can physically touch. Computer software, on the other hand, is not something you can touch. Software is a set of instructions for a computer to perform specific operations. You need both hardware and software for a computer system to work.