The closest we ever get to this situation is when something happens by accident.(The closest 是形容词 形容词前加the可以起名词作用 可以作主语 The closest是主语 we ever get to this situation是定语从句
The closest 是主语we ever get to this situation是定语 is是主句的系动词 后面是表语从句作表语 when something happens by accident.
这个句子是复合句 主系表 结构