improve: the general term, applies to what is capable of being made better whether it is good or bad: measures to ~ the quality of medical care.   (quality表质量时单数)


better: a more vigorous and homely term,differs little in meaning: immigrants hope to ~ their lot in life.


help: implies a bettering that still leaves room for improvement: a coat of paint could ~ the house.


ameliorate: implies making more tolerable or acceptable the conditions that are hard to endure: a cancerous condition that cannot be ~d by chemotherapy.


improve: 通用，任何改善，无论现状好坏，better: 意思相同，较口语化，help: 暗指还有改善空间，ameliorate: 稍微好一点(现状难以忍受)


记忆方法： 1）首字母联想，IBHA联想成BIanHAo变好<==改善         前两个词通用，后两个词暗示情况不好

                 2）改善的意思是使变好(更符合标准更易接受)mean to make more acceptable or bring nearer some standard.