当全班同学都去郊游时，他成了教室里唯一被留下的学生。

He was the only ___left-behind student in the classroom when the whole class went on a field trip.

这个小镇在经济发展中被落在了后面。

This small town has been ___left behind in economic development.

搬家时我的旧相册被遗忘在了角落。

My old photo album was ___left behind in the corner when we moved.