voluntary: implies freedom and spontaneity of choice or action without external compulsion: ~ enlistment in the armed services.      voluntary army志愿军，本例志愿入伍，又如a voluntary [=volunteer] association/organization志愿者协会/组织，a voluntary agreement/retirement/donations/decision自愿协议/退休/捐赠/决定，名词volunteer志愿者，如March of the Volunteers是我国国歌


intentional: stresses an awareness of an end to be achieved: the ~ concealment of vital information.    (aware知道觉察  知道目的即想要达到目的)  


deliberate: implies full consciousness of the nature of one's act and its consequences: the ~ sabotaging of a nuclear plant.    (conscious知道意识到，等于上一词的aware)


willful: adds to deliberate the implication of an obstinate determination to follow one's own will or choice: ~ ignorance.    (obstinate determination to follow...固执己见)


willing: implies a readiness and eagerness to accede to or anticipate the wishes of another: a ~ accomplice in a bank robbery.     （accede to同意、让步） （anticipate预先考虑并满足what Jeff did was to anticipate my next question杰夫预先回答了我的下一个问题）


voluntary志愿自愿: 表示自由自发，不受强迫，intentional有意: 想要达到目的，deliberate故意: 明知自己行为的性质后果，willful执意: 增加了固执己见的意思，willing愿意乐意: 指积极满足他人的愿望或需求


记忆方法: 1) 首字母VIDWW想成I Will Work Very Diligently我将非常勤奋工作<==自愿

               2) 自愿的意思是出于自己的意志或愿望mean done or brought about of one's own will.首字母VIDWW想成I Will Work Very Diligently我将非常勤奋工作<==自愿