Utilize the input text as a context reference, choose the right relationship between 'Airbus' and 'aircraft' from the options.
Options: platform, manufacturer, product/material produced, stock exchange

The slump in sales of very large aircraft has raised questions about how long Boeing and European rival Airbus Group NV can keep building double-decker planes, with 2015 a make-or-break year for both.
product/material produced