What textual evidence gives the best clue to the theme?

a.
"Voters also had to pass a literacy test to prove that they could read, write, and understand the U.S. Constitution."

b.
"It all started on a bus."

c.
"If you happened to be an African American, you had to sit in the back of the bus, even if there were empty seats up front."

d.
"Blacks and whites did not attend the same schools, worship in the same churches, eat in the same restaurants, sleep in the same hotels, drink from the same water fountains, or sit together in the same movie theaters."​