The passage discusses the importance of measuring the health of wildlife and natural resources in financial terms to persuade people like the Hammonds of their value. It emphasizes that the government should not give in to the idea that the living environment is less important. The main idea revolves around the financial valuation of natural resources to highlight their importance, making option A the correct answer. Options B, C, and D, while related to the passage, do not capture the main idea as accurately as option A.