U字开头的单词或词组
USAunableup to nowup-to-dateulcerative colitisunfortunatelyunexpectedlyU-turnustinultimatelyusingunitaryunrecognized commandunderlyingunityUFOuncertaintyup to dateuntitledubiquitousU.K.uncertainuserunlessuptakeundermineunpackunder wayUnited Nationsurnupside downunderstandingunblockupsideUNOumpunauthorizedUHFunfortunateunveilundertakeunrestrained