不眠之夜 white night　
不明飛行物 unidentified flying object (UFO)
不拿原則換人情 refrain from seeking personal favor at the expense of principle
補(bǔ)缺選舉 by-election
不惹是非 Stay out of trouble.; Let sleeping dogs lie.
不速之客 gate-crasher
不惜一切代價(jià) spare no effort; go all out; do one's best
不信任投票 vote of non-confidence
步行街 pedestrian street
步行天橋 pedestrian overpass
不夜城 "sleepless city, ever-bright city"
不以物喜，不以己悲 not pleased by external gains, not saddened by personnal losses
不遺余力 spare no effort; go all out; do one's best
部長(zhǎng)級(jí)會(huì)議 ministerial meeting
不正當(dāng)競(jìng)爭(zhēng) unfair competition
不正當(dāng)競(jìng)選 illicit competition
不正之風(fēng) bad (harmful) practice; unhealthy tendency
步兵師 infantry division
不倒翁 tumbler; never-fall doll
不擴(kuò)散核武器條約 Treaty on the Non-Proliferation of Nuclear Weapons; NPT