The shortcut key for undo is:

A. CTRL+D
B. CTRL+Z 
C. CTRL+O
D. CTRL+U

🧠 Explanation:

The shortcut key for undo in most programs is Ctrl+Z. It reverses the last action, like deleting text or changes. Knowing this shortcut saves time for students or professionals working on computers, making editing in documents or software easier.