1. never trouble trouble till trouble troubles you.
　　麻烦没来找你，就别去自找麻烦。
　　第一、四个trouble是动词，第二、三个trouble是名词。
　　2. i think that that that that that student wrote on the blackboard was wrong.
　　我认为那个学生写在黑板上的那个“that”是错误的。
　　第一个that是连词，引起宾语从句；第二、五个that是指示代词“那个”；第三个that在这儿相当　　于名词；第四个that是关系代词，引起定语从句。
　　3. i know. you know. i know that you know. i know that you know that i know.
　　我知道。你知道。我知道你知道。我知道你知道我知道。