In the passage from President Obama's speech at Selma, the correct rhetorical techniques used are:
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Allusion - President Obama makes references to Scripture and historical events, which serves to connect the civil rights movement to larger themes of faith and perseverance.
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Anaphora - The repetition of phrases, particularly in the context of "they marched as Americans" and "they were called" creates emphasis and reinforces his points about the dedication and struggles of those who marched.
So the two correct answers are: allusion and anaphora.