What impact did railroads have on cities across the United States at the turn of the 20th century?

A.

Many cities became industrial centers.

Explanation:

answer; /// the correct answer is evidence of the olmec civilization has been found in southern american in a hot steamy forest, archaeologists have found earthen artifacts at several sites that were evidence of the olmec civilization. these   artifacts were mounds,courtyards and pyramids build of stones, also on top of the mounds were many monuments made of stone, some of these stone structures are very large, they weigh as much as 44

barack obama

44th president of the united states