U字开头的单词或词组
up to nowunableup-to-dateulcerative colitisUSAunfortunatelyU-turnunexpectedlyustinultimatelyusingunrecognized commandunitaryunderlyinguncertaintyUFOunityuntitledup to dateU.K.ubiquitousuncertainunlessuseruptakeUnited Nationsundermineunpackurnunder wayupside downunderstandingunblockupsideUNOumpunauthorizedunfortunateunveilUHFunrestrainedunfolding
