A research team examined a long-term owl roost. Owls prey on small mammals and the excreted remains of those meals that accumulated. over the time, provide us an insight into the composition and structure of small mammals over the past millennia. The research suggested that when the Earth went through a period of rapid warming about 13,000 years ago, the small mammal community was stable and resilient. But, from the last quarter of the nineteenth century, human-made changes to the environment had caused an enormous drop in biomass and energy flow. This dramatic decline in energy flow means modern ecosystems are not adapting as easily as they did in the past.

Correct Option (B)

Assumption 3 is valid. The passage explicitly states that "from the last quarter of the nineteenth century, human-made changes to the environment had caused an enormous drop in biomass and energy flow. This dramatic decline in energy flow means modern ecosystems are not adapting as easily as they did in the past." This directly implies that human activities are responsible for the diminished adaptive capacity, or natural resilience, of Earth's ecosystems.

Incorrect Options:

• Assumption 1: "Global warming is a frequently occurring natural phenomenon." The passage mentions a single instance of rapid warming approximately 13,000 years ago, which was a natural event. However, it does not provide information to conclude that global warming is a "frequently occurring" natural phenomenon in general.
• Assumption 2: "The impending global warming will not adversely affect small mammals." The passage suggests the opposite. It highlights that while small mammal communities were resilient to natural warming in the past, modern ecosystems, due to human-made changes, are now struggling to adapt. This indicates that current environmental changes, including global warming, are likely to have adverse effects.