Answer:
3.to provide evidence
Step-by-step explanation:
According to the paragraph, Jefferson believed that the American's mockingbird was superior to other birds because of its melodious voice and tone.
The documents in the form of letters and journal entries provide evidence for Jefferson's beliefs. If someone begins to dispute that Jefferson actually had such beliefs, the documents would serve as evidence to verify or confirm that Jefferson indeed believed that the American's mockingbird was superior to others.