before引导的是时间状语，表示在......之前，后面跟完整句子，是时间状语从句。例如三思而行的英语有think twice before you jump。
I had lived here for three years before he came here.在他来这之前，我已生活在这三年了。
I must arrive at cinema before my girlfriend arrives.我必须在我女朋友到达之前到达电***。
Knock on even a stone bridge before you cross it.Better safe than sorrylook before leapThink twice before acting/you do it 以上都是三思而后行,比较地道的说法.I h***e decided to go the south to start over我决定去南方闯一闯Think twice before acting要三思而后行啊.
