Task: Question Generation
Input (English): The Earth contains about 434 billion cubic meters of growing stock forest, 47% of which is commercial. As an abundant, carbon-neutral renewable resource, woody materials have been of intense interest as a source of renewable energy. In 1991, approximately 3.5 cubic kilometers of wood were harvested. Dominant uses were for furniture and building construction.
Output (English): About how many cubic kilometers of the vast stock forest's wood were harvested in 1991?