Concept:The keyboard shortcut command used to restart a computer is the three-key combination
Alt+Ctrl+Del.
Explanation:First, option A is
Ctrl+S, which is commonly used to save a file, not to restart the computer.
Second, option B, usually written as
Ctrl+O, is used to open a file or document, so it is not correct.
Third, option C,
Del+Alt+S, is not a recognized keyboard command for restarting a computer.
Finally, pressing
Alt+Ctrl+Del interrupts the current operation and opens the system security screen.
From that screen, the user can choose to restart the computer or open the Task Manager.
This is the standard shortcut used in Windows and many older systems for restarting.
Therefore, the correct answer is option D.
Answer:D. Alt+Ctrl+Del