1.in +一段時(shí)間 用于將來(lái)時(shí),e.g
He will come back in three days.
2.一段時(shí)間+later 用于過(guò)去時(shí),e.g
Three days later,he came back.那么after 呢after+一段時(shí)間，也用于過(guò)去時(shí)，e.gAfter three days ,he came back.