Riddle

What becomes white when it is dirty?

Choose an answer

A.Snow
B.Chalk
C.Whiteboard
D.Blackboard
Hint: It's a word with 10 letters, starting with "B".

Answer

Blackboard

Why this is the answer

A blackboard turns whitish as chalk dust builds up on it -- the more it is used ("dirtied"), the whiter it looks.

This riddle is filed under Hard/Difficult Riddles and rated Medium.