他在数学课上总是跟不上进度。

He is always ___lagging behind in math class.

由于网络问题，视频会议的画面总是延迟。

The video conference keeps ___lagging due to network issues.

工人们在锅炉上安装了保温层以减少能量损耗。

The workers installed ___lagging around the boiler to reduce energy loss.