"I shall try to find out how the forces of nature interact upon one another and how the geographic environment influences plant and animal life. In other words, I must find out about the unity of nature." What do these sentences reveal about Humboldt?
A. Humboldt wished to change geographic boundaries in order to promote biological diversity.
B. Humboldt believed that his trip would be a pivotal moment to bring people together.
C. Humboldt was motivated by a desire to discover new areas for settlement.
D. Humboldt saw his expedition as a unique opportunity to learn more about the physical world.