Which of the following shortcut keys is used to switch between open applications in Windows?

Correct option is A

The correct answer is (a) Alt + Tab
Explanation:
• Alt + Tab cycles through open application windows in Windows OS, allowing quick switching.
• Alt + F4 (c) closes the current window.
• Alt + Shift + Tab cycles in reverse.
• Widely supported across Windows versions.
Information Booster:
• On macOS the analogous shortcut is Command + Tab.
Additional Knowledge:
(b) Alt + Ins — context/insert in some editors.
(d) Alt + Del — not a standard switch shortcut.