轻松学英语：900句:旅途防盗Guard Against TheftTom:Where is my backpack?
Marry:I don't know.
Where did you leave it?
Tom:I just put it on the chair a while ago, but now it's gone.
Marry:Are you sure?
Tom:Of course, I'm sure.
I bet someone stole it.
Marry:Well, you should've kept an eye on it.