Thinking--- you know--- in fact you don’t is a terrible mist

Thinking___ you know___ in fact you don’t is a terrible mistake.希望能够提供句子成分的分析,A.that; that B.what; what C.that; what D.what that句子中主语“Thinking__of_ you know__that_ in fact you don’t”的具体成分是什么，