Despite the ratification of the fourteenth and fifteenth amendments, many southern states kept african americans from exercising their right to vote during the "jim crow era." why were they able to do this? (a) southern states passed laws that superseded federal laws.(b) the federal government did not adequately enforce the amendments.(c) african americans did not try to vote because they did not believe their votes would count.(d) the southern states did not ratify the amendments so they did not have to follow them.