"They tend to be people with deep roots in the city, who have hung around since before the neighborhood became what it is today," he adds.
“他们往往是在这座城市根基深厚的人,那些在这个社区变成今天这个样子之前就一直在这里的人,”他补充道。
时间状语从句,"since" 引导,修饰 "have hung around"。从句内部是 "before the neighborhood became...",before 引导的时间状语从句嵌套在 since 从句中,形成 "since before" 的双重时间结构。"became" 后接表语从句 "what it is today"。