effective: stresses the actual production or the power to produce an effect: an ~ rebuttal.   有效的反驳


effectual: suggests the accomplishment of a desired result or the fulfillment of a purpose especially as viewed after the fact: the measures to halt crime proved ~.    halt完全停止to stop completely，军事上叫立定，短语to come to a halt终结      可见这个词和effective意思基本相同，只是程度更高


efficient: suggests an acting or a potential for action or use in such a way as to avoid loss or waste of energy or resources in effecting, producing, or functioning: an ~ small car.   小型节能车   energy能源能量，resource资源


efficacious: suggests possession of a special quality or virtue that gives effective power: a detergent that is ~ in removing grease.


effective有效: 强调实际产生了效果，effectual有成效: 表示成功实现了想要的结果目标,特别是从事后来看，efficient高效节能: 表示操作使用时不浪费损失能量资源，efficacious特效: 具有产生效力的特质特长


记忆方法: 1）首字母4E四个效果多快好省<==有效        "多快好省"可能只是个理想，有人曾说: "多了就不能快，好了就别想省"--想取得好的结果，只能多投入时间精力

         2）有效的意思是能产生效果mean producing or capable to produce an effect.       effect效果: 跟随起因的事物implies something that follows a cause，另外effect和cause是固定搭配表示因果关系cause and effect，如the effects of radiation on the body辐射对身体的影响（效果）