He remembered to post a present to his mother for her sixtieth birthday. Why not use ‘posting’ instead of ‘to post’?
I think posting is better. But the book use ‘to post’, I feel it weird.
"Remembered to post" and "remembered posting" have different meanings. To remember to do something means to not forget to do something important or necessary, for example posting a present to one's mother in good time for her birthday. To remember doing something simply means to recall doing something.