Passage Summary: Plants soak up CO2 when they grow fast but leak it when they grow slow. More CO2 makes the tropics hotter, and that heat makes the plants there grow slower.

Reasoning: Fast-growing plants absorb CO2, while slow-growing ones release it; increased CO2 raises tropical temperatures, which in turn causes tropical plants to grow more slowly.

Analysis: This stimulus describes a classic positive feedback loop where the effect reinforces the cause. If CO2 increases, temperatures rise, causing plants to grow slower; because slow-growing plants release CO2, this will lead to even more CO2 in the atmosphere. You should look for an answer choice that synthesizes these facts, likely pointing toward the conclusion that rising temperatures in the tropics will eventually lead to even higher levels of atmospheric carbon dioxide.