Answer:
option a, she refused to remove to the train car designed for african Americans.
The U.S economy produce 20% of the world's output
A cold front<span> is the transition zone where a </span>cold<span> air mass is replacing a warmer one
</span>T<span>hey move more slowly than warm fronts.</span>
Because other three are characteristics of the cold front and they move faster than warm
so option D is correct
hope it helps