D
B和D有区别,忘记已做某事,用forget doing,即forget后面加动名词,如：
Shall you ever forget hearing her sing?
Never shall I forget hearing her sing.
I forget posting it.
I forgot (about) doing it.
forget后接动词不定式表示忘记去做某事的意思,也就是说这个事情没有做.比如：
I forgot to buy the book that you recommended.
He forgot to return the money that he had borrowed.
This is the third time I have forgotten to use "the" before the word "sun".How careless of me it is!
希望我能帮助你解疑释惑.