小川里沙
首先，三者都有“提前”的意思。in advance 常置于句尾,常常是提前做某事。例：It is cheaper if you book the tickets in advance.ahead of time 强调的是提前了具体的某一小个时间段，例：He arrived ahead of time, and had to wait. ahead of schedule 强调的是比原计划，原进度提前了，句子的主题是一项任务类的事情例：We finished the project ahead of schedule.
