Answer:
Ethos, because she is using her own knowledge as a tool.
Step-by-step explanation:
Harriet Tubman was an activist and served as a spy for Union Army. 'Harriet Tubman: Conductor on the Underground Railroad' is a book written by Ann Petry narrating the accounts of life of Harriet Tubman who helped free 300 slaves using the paths of Underground Railroad.
In the given excerpt, Tubman has used the rhetorical appeal of 'ethos' as she is using her own knowledge as a tool. While rescuing slaves using Underground Railroad, Tubman made up several stories to keep the slaves moving and encourage them in their paths of freedom. The path for freedom was dangerous, and Tubman knew that some may back up from this, so she kept telling them about people who chose to struggle for freedom, made up stories about them and used this knowledge as a tool to keep the slaves encouraged and motivated. And no one asked her even one question as they trusted her (credibility-- element of ethos).
Thus, the tool Tubman has used in the given excerpt is ethos.