U字开头的单词或词组
undertakingunrelentingusurpunregisteredunsuspectedunspoiltunconditionalultimatumunboundunerringuneventfulunbalancedunfavourableupkeepUPSupstartundefined variableunderstandablyUFPup forurethaneunresolvedupdate nowunder one's beltuglinessunreasonableuntrueU.S.S.R.unlinkunfilledunaccustomedunderwaterukuleleunorganizedundressunsungupturnungratefulunidentifiedunevenUCLunder control
