ok.看下面的句子：
They say that the accident / incident happened in 2007 when both of them were on holiday in California(宾语从句)-----变成简单句结构就是：The accident /incident is said to have happened in 2007 when both of them were on holiday in California.这里主句中say 指代现在.从句中的happened指代过去.---------在这种情况下,变成简单句时就成了to have happened：
The work is said to have been done yesterday.-----------记住：简单句的时候,用今天的眼光看过去的事情,过去的事情就用 （to）have (been) done的结构.又如：
They say she was here last week == she is said to have been here last week.