one focuses on changes in breathing during exercise while other on changes in heart rate
The correct answer in this question is a
1) when slavery was abolished at the end of the Civil War, southern states created back codes,laws which aimed to keep white supremacy in place
2) Black codes attempted to economical disable freed slaves ,forcing African Americans to continue work on plantations and to remain subject to racial hierarchy within the southern society.
3) Black codes gave rise to a new wave of Radical Rebublicanism in Congress, and the eventual move towards enshrining racial equality into the Constitution. However, black codes also set precedent for Jim Crow laws.
-hope that helps...
The answer is A, sound waves travel the quickest through solids, then air, slowest through liquid