Okay, the user wants me to translate "narrow-bodies" into Traditional Chinese. Let me think about the correct term here. In aviation, "narrow-body" aircraft typically refers to planes with a single aisle, like the Boeing 737 or Airbus A320. The term "narrow-body" is often translated as "窄體客機" in Chinese. Since the user specified Traditional Chinese, I should use the traditional characters. Let me double-check if there's a more standard translation. Yes, "窄體客機" is the correct term. Also, the user mentioned that if the content is already in Traditional Chinese, leave it as is. Since the input is in English, I need to translate it. No explanations, just the translation. So the answer should be "窄體客機".