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

• knobby
• knock
• knockabout
• knock-back
• knock-down
• knocker
• knocking shop
• knock-on
• knockout
• knock-up
• knoll
• knot
• knotty
• know
• know-all
• know-how
• knowingly
• knowledge
• knowledgeable
• known
• knuckle
• knuckle-dragger
• knuckleduster
• knucklehead
• knuckle sandwich