a. 忘不了的, 令人难忘的

forget/unforgettable/remember/memory/memorial/memorandum/mental/monument/forgive
记忆：
1． forget [ fE5^et ] vt. 忘记, 忽略 You have forgot to turn the light off again!你又忘了关灯！ forget to do sth. 忘了做某事；forget doing sth. 忘了做过某事
2． forgetful [ fE5^etful ] adj. 健忘的, 易忘的 What a forgetful man he is!他是个多么健忘的人啊！
3． unforgettable [ 5QnfE5^etEbl ] adj. 忘不了的, 令人难忘的 Everyone has his unforgettable experiences no matter they are pleasant or shameful.每个人都有其难忘的经历，不管它们令人愉快还是令人羞愧。
4． 词根mem [mem] men表示“大脑”，remember [ ri5membE ] 回到脑海中， vt.回忆起, 铭记, 纪念 Remember to come in time next time!记住下次来时要及时。remember to do sth.记得要做某事；remember doing sth. 记得做过某事。