+in There has been a steady decline in public services over recent years. 近几年公共服务的质量一直在持续下降。

a sharp/steep/dramatic decline a sharp decline in share prices 股票价格的急剧下降

economic/moral decline an effort to halt the economic decline of the region 阻止该地区经济衰退的努力

fall/go/slip into a decline The industry has now fallen into a decline. 这个行业现在已不景气了。

in decline Agriculture is in decline in many Third World countries. 许多第三世界国家的农业都在衰退。

on the decline Thankfully, this is a disease that is now on the decline. 令人欣慰的是，这是一种现在越来越少的疾病。