in加時(shí)間段,用于將來時(shí),表示將來一段時(shí)間后.而after加時(shí)間段,用于過去時(shí),表示從過去某個(gè)時(shí)間點(diǎn)算起一段時(shí)間后.另外,after還可接時(shí)間點(diǎn),既可用于將來時(shí)也可用于過去時(shí).例：
He will be back in three days.他三天后會(huì)回來的.
He came back after three days.他三天后就回來了.
He came back after two o'clock.他兩點(diǎn)后回來了.
He will come back after two o'clock.他兩點(diǎn)后會(huì)回來的.