Must be false. We know that Marvel’s sales remained constant while their market share decreased following the emission standards. (This means, for example, that their market share went from 50% to 25%, but they still sold the same number of new cars.) This requires that sales of other companies increased. So it's impossible for sales from other companies to have decreased following the emission standards.

Could be true. We know that Marvel’s market share doubled during the ten-month period before the emission standards were imposed. It is possible that during this time other companies’ market share decreased.

Could be true. We know what happened following Calistan’s imposition of emission standards. But we cannot be certain about what would occur without these emission standards. Perhaps without emission standards Marvel would have lost even more market share.

Could be true. We know what happened in the three months following imposition of the standards. But we don't know what will happen in the future.

Could be true. We know that Marvel’s monthly sales remained constant following the emission standards. But this doesn't tell us what happened to Marvel's average profit on new cars sold. Maybe they reduced their production costs and earn more per car.