Passage Summary: In Country Q, the amount of coal sitting around—already dug up but not yet used—dropped significantly between 1990 and 1991, and they didn't trade any coal with other countries.

Reasoning: The stock of available coal (mined but not consumed) decreased from the end of 1990 to the end of 1991, and no coal entered or left the country's borders.

Analysis: This stimulus is essentially a math problem regarding inventory. The 'total available supply' is the stockpile of coal already mined; if that stockpile decreased over the year and no coal was imported or exported, the 'outflow' must have exceeded the 'inflow.' Specifically, the amount of coal consumed in 1991 must have been greater than the amount of coal mined during that same year. Any valid inference must respect this balance of mining versus consumption.