The question is about identifying the main idea of a reading passage. The correct answer is B, 'The adaptability of certain species over time', as it directly relates to the concept of species surviving for millions of years. Option A focuses on conservation efforts, which is not the main idea if the passage is about survival over time. Option C is about climate change, which could be a factor but not the main idea. Option D is about evolution, which is a broader concept than the specific idea of survival over time.