Passage Summary: Tiny organisms in certain rocks eat organic matter, which uses up oxygen and creates carbon dioxide; these organisms also multiply faster when it gets warmer.

Reasoning: N/A

Analysis: We are looking for a statement that must be true based on the combination of these facts. The stimulus sets up a potential positive feedback loop: the microbes produce carbon dioxide (a greenhouse gas), which raises temperatures, which in turn causes the microbes to reproduce faster and produce even more carbon dioxide. Look for an answer that synthesizes these causal steps into a single prediction about accelerating global warming or increasing CO2 levels. Avoid any answer that introduces outside information not found in the text.