https://online2.tingclass.net/lesson/shi0529/0009/9907/629.mp3
https://image.tingclass.net/statics/js/2012
behind one's back 在某人之背后,背著某人,背地里
They did it behind Mike's back.
他們是背著麥克做的這件事。
What? You ate up everything behind my back.
什么,你居然背著我把所有東西都吃光了。