do not forget___(post)the letter for me when you pass the post office.

do not forget___(post)the letter for me when you pass the post office.
do not forget___(post)the letter for me when you pass the post office.

do not forget___(post)the letter for me when you pass the post office.
to past

to post
forget to do 是忘记去做某事
forget doing是忘记做了某事
如果不是这样，就是相反的……