The correct answer is C. program.
A general-purpose computer is a computer that can be programmed to carry out a wide range of tasks. This is in contrast to a special-purpose computer, which is designed to perform a specific task.
General-purpose computers can be adapted to countless uses simply by changing their program. For example, a general-purpose computer can be used to write a document, create a spreadsheet, or play a game.
The other options are incorrect because they do not affect the overall functionality of a computer. A keyboard is used to input data into a computer, a printer is used to output data from a computer, and a display screen is used to display data from a computer.
However, the program that is running on a computer determines what tasks the computer can perform. By changing the program, you can change the function of the computer.