- He never remembers 1. _______ his mother a birthday card. It has been so long since he did it that she can't remember ever 2._RECEIVING_one from him
Could it be in 1 sending: I know the solution is to send but I think sending could make it too because he did send... may be a long time ago but he did it.
I know the difference between "remember to" or "remember gerund" but in this particular case I think both can fit. I don't see a real difference.