Okay, the user wants me to translate "sub-grade" into Turkish. Let me check the rules again. The first rule says to translate all content into Turkish. The second rule states that if the content is already in Turkish, leave it as is. The third rule is to provide only the translation without any explanations.
So, "sub-grade" is an English term. I need to find the correct Turkish equivalent. "Sub-" as a prefix can mean "alt" or "alt seviye" in Turkish. "Grade" can be translated as "seviye" or "derece" depending on context. In academic contexts, "grade" is often "seviye" or "not". But "sub-grade" might be a technical term. Let me think. In some contexts, like in education, a sub-grade could be a lower level or a subdivision of a grade. So "alt seviye" might be appropriate. Alternatively, "alt derece" could work. However, I should check if there's a standard translation for "sub-grade" in Turkish. If there's no direct equivalent, maybe "alt seviye" is the safest choice. The user didn't provide context, so I'll go with the most common translation. Therefore, the translation is "alt seviye".