If you understand

If you understand , say &#;&#;understand&#;&#;. If you don&#;t understand, say &#;&#;don&#;t understand&#;&#;.But if you understand and say &#;&#;don&#;t understand&#;&#;. how do I understand that you understand . Understand?
如果你知道就說“知道”， 如果你不知道就說“不知道”；如果你知道卻說“不知道”， 我怎么知道你知道，知道嗎？