Answer: D. People who disagree with his ideas about nature.
Explanation:
The author is mostly trying to reach people who disagree with his ideas about nature. This is the reason he is letting them know about his bias from the beginning. The author believes that people who disagree with him might accuse him of being biased, and therefore, of having a less trust-worthy opinion. He deals with this by disclosing it from the beginning, and therefore, avoiding such accusations.
