What is clean when it is blanck and dirty when it is white?

what is black when it is clean and white when it is dirty是-- What is clean when it is black and dirty when it is white? What is black when it is clean and white when it is dirty? what is black when it is clean and white when it is dirty?用英 What is biack when it is clean and white when it is dirty? 脑筋急转弯：1 What's black when it is clean and white it is dirty? What is black when it is clean white when it is dirty? That is black when it is clean and white when it is dirty What、is、black、when、it、is、clean、and、when、it、is、dirty·谜底是什么? what is biack when it is ciean and white when it is dirty?(翻 it is clean when it is black.it is dirty when itis white.wha 智力测试What is black when it is clean and white when it is dirt