I'm sorry that I forgot _____(send) your letter.

I'm sorry that I forgot _____(send) your letter.
I'm sorry that I forgot _____(send) your letter.

I'm sorry that I forgot _____(send) your letter.
to send

forget to do sth 忘记做某事



希望能帮到你,祝更上一层楼O(∩_∩)O
有不明白的请继续追问(*^__^*)

to send

sending