3. What structure would a writer use to show both similarities and differences
between two things?

If I understand the question correctly, I would say:

a comparison-contrast structure

Explanation:

answer: the gettysburg address is a speech delivered by abraham lincoln at the november 19, 1863, dedication of soldier’s national cemetery, a cemetery for union soldiers killed at the battle of gettysburg during the american civil war.

explanation:

in the section of speech is not