In 1870,25 American cities had populations over 50,000.
Answer:
b, paintings and sculptures had more realistic human figures
Louisiana Purchase happened in 1803, specifically, July 04, 1803. (but the celebration of July 4 remembers this day in 1776, not 1803)
Gadsden Purchase - December 30, 1853.
The difference is a round 50 years, and more specifically 50 years, 5 months and 26 days!
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The answer is c. A hint would be there is lots of sand there.