U字开头的单词或词组
up-to-dateunableU-turnupstairsurgencyundoubtedlyunexpectedlyunfortunatelyunitaryusinguncertaintyunrecognized commandunderlyingultimatelyU.K.up to dateurnuntitledUFOUnited Nationsunlessupside downunder wayuptakeunblockundermineunderstandingubiquitousuncertainunzipunityumpUNOuserUHFunpackusher inunauthorizeduglifyUSAunder the circumstancesunfolding