problematic：有疑问的，未解决的，未定的 

词根词缀：pro-前 +blem扔,抛 + -atic形容词词尾

• unwilling
• unwind
• unwonted
• unworldly
• up
• upbeat
• upbraid
• upchuck
• upcoming
• update
• upend
• upfront
• upgrade
• upheaval
• uphold
• upholster
• upholsterer
• upkeep
• upmarket
• upon
• upper
• uppity
• upraised
• upright
• uprightness