Passage Summary: Elephant ivory is illegal but mammoth ivory is legal. When the ban started, people claimed they were importing mammoth ivory, but as soon as a test was created to tell the difference, those 'mammoth' imports suddenly stopped.

Reasoning: After elephant ivory was banned, imports of ivory labeled as mammoth ivory increased; however, once a test to distinguish the two was publicized, those imports dropped significantly.

Analysis: This set of facts points toward a strong circumstantial inference regarding the behavior of importers. The sharp decrease in 'mammoth' ivory imports immediately following the introduction of a reliable identification technique suggests that much of the previously imported ivory was likely mislabeled elephant ivory. When the risk of being caught increased, the incentive to attempt the fraud decreased. Look for an answer choice that identifies this likely deception or the effectiveness of the new testing method in deterring illegal trade.