谜底：a blackboard
谜语：What is black when it's clean and white when it's dirty?
谜语：What is black when it's clean and white when it's dirty?
谜语推荐
- what's too much for two and just right for one?
- a red coat, white body and black heart.
- what is black when it's clean and white when it's dirty ?
- It has red face,and green leaves
- What is the smallest bridge in the world?
- it’s a furit. it’s also a color. what is it?
- What never asks questions but gets a lot of answers?
- What always goes up and never goes down?
- What has a tongue but cannot talk?
- what man cannot live in a house?