it is clean when it is black.it is dirty when itis white.what is _英语解答

it is clean when it is black.it is dirty when itis white.what is it

人气：117 ℃　时间：2019-12-29 22:14:37

解答

干净的时候是黑的,脏的时候是白的,这是什么东西呢?
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