Passage Summary: Big tropical fires in 1997 were caused by a drought from El Niño, and scientists think air pollution made that El Niño particularly strong through global warming.

Reasoning: In 1997, El Niño caused a widespread drought that made the tropics susceptible to intense forest fires; additionally, many scientists link the strength of that El Niño to pollution-induced global warming.

Analysis: Since this is a 'Must be True' question, we need to find a synthesis of the provided facts without adding outside information. We can trace a causal chain: Pollution/Global Warming (potentially) -> Stronger El Niño -> Drought -> Susceptibility to Fire. We can safely infer that the 1997 fires were at least partially a result of the weather patterns caused by El Niño. Look for an answer that stays within the bounds of these relationships, likely connecting the environmental conditions of 1997 to the resulting fires.