(1)I forgot_posting__(post)the letter and thought I had left it at home.
(2)Please post the letter for me.I forgot__to post_(post) it this moring.
forget to do 忘記要去做某事.(未做)
forget doing 忘記做過(guò)某事.(已做)
The light in the office is stil on.He forgot to turn it off.
辦公室的燈還在亮著,它忘記關(guān)了.(沒(méi)有做關(guān)燈的動(dòng)作)
He forgot turning the light off.
他忘記他已經(jīng)關(guān)了燈了.( 已做過(guò)關(guān)燈的動(dòng)作)
Don't forget to come tomorrow.
別忘了明天來(lái).(to come動(dòng)作未做)