回复：启蒙性教育第一课昨晚通过

My daughter is 8, she asked me the same question again a couple of days ago. Before I could answer it,she gave me answer by herself. Since one time when we were waiting long hours at the emergency room, she read some magazines available there. One of them was "Parenting" something, just talked about this kind of issue. Expert told parents the answer is'"Daddy has something like a puzzle piece can just fit into Mommy." And she is satisfied with that answer. It's a hard task, even they are studing human body and systems at school, but teacher avoided reproductive system too.(I thought American school would do something differently from Chinese school.)