lessen decrease degrade reduce 区别

虽然都是减少的意思,但是还是有少许的差别
lessen的意思是减轻,比如说减轻痛苦,减轻疼痛,减轻影响.using radar sensors and cameras to predict a crash and help lessen the impact and injury, or possibly even avoid an accident altogether.
decrease的意思是量上的减少 ,客观的,The amount of homework decreased towards the end of the semester
degrade意思是降级,退化,恶化.比如说环境恶化.
reduce的意思是也是减少,但是是主观的,认为的减少