which is black when you buy it,red when you use it,and gray when you throw it away?

Which is ciean when it is black and dirty when it is white? which is black when you buy it,red when you use it,and gray when you throw it away?猜一猜: which is black when you buy it,red when you use it,and gray when you throw it away? Which horse is s( The black one Which horse is s( The black one （英语谜语）which is black when you buy it,red when you use it,and gray when you throw it away In South Africa,English is the language _______ black parents wish their children to be educated A.for which B.that C.in which D.when it is clean when it is black.it is dirty when itis white.what is it It is clean when it is black.It is clean when it is black.It is dirty when it is white.what's it? 智力测试What is black when it is clean and white when it is dirty? What is clean when it is black and dirty when it is white? What is black when it is clean white when it is dirty? what is black when it is clean and white when it is dirty是----- What is black when it is clean and 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 clean when it black ,and white when it is dirty. 猜谜语：It is clean when it is black.It is dirty when it is white.What's it