As a senior student, you are supposed to know better than just____ until the examination.A. fooled aroundB. to fool aroundC. having fooled aroundD. to have fooled around

本题考查固定搭配的用法。解题的关键在于熟悉“know better than to do sth.”这一固定表达。

“know better than to do sth.”是一个常用的固定短语，意思是“明事理而不至于做某事；很明智而不会做某事”。在这个短语中，to do sth. 是固定的结构形式。

在本题中，“As a senior student, you are supposed to know better than...”表达的是作为一名高年级学生，应该明白事理而不至于做某事。所以后面需要接动词不定式“to fool around”。

选项A“fooled around”是过去式或过去分词形式，不符合“know better than to do sth.”的结构要求；选项C“having fooled around”是现在分词的完成式，也不符合该固定搭配；选项D“to have fooled around”是动词不定式的完成式，同样不符合此固定结构。