Passage Summary: Animals need plants to stay alive, but plants also need animals to help them reproduce and to keep the air filled with the carbon dioxide they need.

Conclusion: The relationship between plants and animals is characterized by mutual dependence.

Reasoning: Animals require plants for survival, while plants rely on animals for reproduction through pollination and seed dispersal, as well as for the carbon dioxide produced by animal respiration.

Analysis: To identify the conclusion here, notice how the passage is structured around the word 'mutual.' The first sentence acknowledges animal dependence on plants, but the rest of the stimulus is dedicated to proving the reverse: that plants also depend on animals. This makes the statement about mutual dependence the central point that all other facts support. When evaluating the choices, ensure you pick the one that encompasses both sides of the relationship rather than just a specific example like pollination or CO2.