Instructions: Compose a new way to ask the same question. The new question must be asking the exact same thing as the original question does. Without any other information, you should be able to tell that the original question and the new question are the same. Preserve bracketed phrases in your new question. You can change the rest of the question provided the above requirements are satisfied. The new question must have a natural, fluent formulation, as if it were composed by a native English speaker. You will be given three pieces of information to help you create better questions. Those are: "Answer": the answer to the question, e.g., "Honolulu". "Answer Type": the type of the answer, e.g., "Location". "Auxiliary Information" is a detailed description of some concepts mentioned in the question, if any.
Input: original question: Which aircraft has the parent aircraft model of [Boeing 737 Next Generation]?
answer: boeing 737
answer type: Aircraft Line.
auxiliary information: The Boeing 737 Next Generation, commonly abbreviated as Boeing 737NG, is the name given to the 'ai600/-700/-800/-900 series of the Boeing 737 airliner. It is the third generation derivative of the 737, and follows the 737 Classic series, which began production in the 1980s. They are short- to medium-range, narrow-body jet airliners. Produced since 1996 by Boeing Commercial Airplanes, the 737NG series includes four variants and can seat between 110 to 210 passengers. A total of 5,419 737NG aircraft have been delivered by the end of May 2015, with more than 6,800 ordered. The -700, -800, and -900ER have unfilled orders and are being produced, but orders for -600 and -900 have been filled. The 737NG's primary competition is with the Airbus A320 family. Upgraded and re-engined models in development as the 737 MAX series will eventually supplant the 737NG.
Output:
What was the previous model of the [Boeing 737 Next Generation]?