Passage Summary: Because we find medicine in rainforest plants and haven't even looked at most of them yet, losing the forests means losing the chance to ever make those medicines.

Conclusion: Important medicines will never be created if tropical rainforests are destroyed.

Reasoning: Many medicines come from rainforest plants, and there are thousands of unstudied plants in those forests that likely contain medicinal substances.

Analysis: The argument relies on a significant 'Gap' regarding the exclusivity of these plants. It assumes that the medicinal substances found in the rainforest cannot be found anywhere else or created synthetically. If these same substances existed in common plants outside the rainforest, the destruction of the forest wouldn't necessarily prevent the medicines from being developed. Therefore, the argument 'needs' it to be true that these substances are unique to the rainforest. Look for an answer that addresses this exclusivity.