某人与一老外相撞

某人刻苦学习英语，终有小成。一日上街不慎与一老外相撞，忙说：I am sorry.老外应道：I am sorry too. 某人听后又道：I am sorry three.老外不解，问：What are you sorry for? 某人无奈，道：I am sorry five.