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

• refuse
• refusenik
• refute
• regain
• regal
• regale
• regalia
• regard
• regarding
• regardless
• regatta
• regency
• regenerate
• regenerative
• regent
• reggae
• regicide
• regime
• regimen
• regiment
• normally
• Norman
• Norse
• north
• northbound