However, some parents are concerned that it encourages their children to drop litter so they can watch the birds to pick it up.
2019年12月四級真題（第一套）聽力 Section A
His strange habit makes sense when you consider that he's an environmental scientist who studies how to reduce litter, including things that fall off garbage trucks as they drive down the road.
2018年高考英語浙江卷 閱讀理解 閱讀B 原文
If you love helping the environment, plant trees or pick up litter.