https://online1.tingclass.net/lesson/shi0529/0000/704/1_101.mp3
https://image.tingclass.net/statics/js/2012
M: Where is my back pack?
W: I don't know. Where did you leave it?
M: I just put it on the chair a while ago, but now it's gone.
W: Are you sure?
M: Of course, I am sure. I bet someone stole it.
W: Well, you should have kept an eye on it.