This classic riddle asks: What kind of key can’t open a single door?
The answer is: a keyboard key.
A computer keyboard is full of keys, but none of them are designed to unlock a door.
The riddle works because the word “key” usually makes you think of a metal key used in a lock. But “key” can also mean one of the buttons on a keyboard.
Once you think outside the context of locks and doors, the answer becomes simple.


