Provide the ingredients that are rationed in the recipe with the highest carbohydrate content.
the highest carbohydrate content refers to MAX(carbo)
SELECT T1.name FROM Ingredient AS T1 INNER JOIN Quantity AS T2 ON T1.ingredient_id = T2.ingredient_id INNER JOIN Nutrition AS T3 ON T3.recipe_id = T2.recipe_id WHERE T2.max_qty = T2.min_qty ORDER BY T3.carbo DESC LIMIT 1