Hi kobel51,

This CR prompt focuses on a "causal" argument: the idea that one thing causes another. It's a common logic "structure" that you'll see in some CR questions on Test Day. To figure out the assumption behind the prompt, you'll need to understand the logic first.

The Facts:
-1992: outlaw fishing boats began ILLEGALLY harvesting lobsters around Belukia
-Soon after the outlaw harvesting began, annual tonnage of LEGALLY harvested lobsters began declining
-1996: NO REDUCTION in the level of LEGAL lobster harvesting; the legal catch was 9,000 tons BELOW pre-1992 levels

The Conclusion:
-Outlaw fishing harvested about 9,000 tons of illegal lobsters that year.

The Logic:
The causal argument in this prompt is that the outlaw harvesting was the ONLY reason why the LEGAL harvesting was down 9,000 tons AND ALL of those missing 9,000 tons were harvested by the outlaws. To believe this logic, you would have to assume that NOTHING ELSE factored in to the decrease in legally captured lobster.

Answer A tells us that the something else DID NOT decrease the lobster population, thus giving credence to the idea that illegal outlaw fishing boats were the cause of the 9,000 ton decline.

GMAT assassins aren't born, they're made,
Rich