Three years have elapsed since we left middle school .

自从我们上次见面以来已经过去三年了。

Three years have elapsed since we last met .

自我们上次见面以来，已经过去三年了。

Seven years have elapsed since we married .

自从我们结婚以来，七年过去了。

A long time had elapsed since I had attempted any serious study .

自我试着认真读书以来，很长一段时间已经过去了。

That indicates the time elapsed since the process started .

它指示进程启动后所经过的时间。