Correct Answer:
C. Alt+Tab
In Windows operating systems, the Alt+Tab keyboard shortcut is the standard and most widely used method to quickly switch between currently open applications or windows. Pressing and holding Alt while repeatedly pressing Tab cycles through the open programs, allowing the user to select the desired application. This shortcut is fundamental for efficient multitasking. Shift+Tab is typically used to move backward through elements in a dialog box or web page. Ctrl+Tab is commonly used to switch between tabs within a single application, such as a web browser. Alt+Shift+Tab performs the reverse action of Alt+Tab, cycling backward through open applications.