Final answer:
The author's tone in the excerpt from "The Unseen Values" is best described as reasonable, focusing on the logical presentation of the benefits derived from American space exploration.
Step-by-step explanation:
The choice that best reflects the author’s tone in the passage from "The Unseen Values" is reasonable. The tone of the excerpt indicates a logical presentation of the beneficial outcomes of American space exploration, emphasizing the practical uses and advantages such as national security, a strengthened national economy, new jobs, and technological advancements. The author lists these benefits in a factual and measured manner, showcasing the positive externalities and public goods that come with government investment in innovation, without resorting to emotional or highly charged language.