Sir isaac newton revolutionized the way people understood the universe in the seventeenth century when he proved that the a) earth revolves around the sun. eliminate b) planets revolve around the sun. c) planets are held in place by an invisible shield. d) sun's gravity keeps the planets within their orbits.

C: that the sun's gravity keeps the planets withing their orbits. 

The transcontinental railroad provided a means of fast transportation. it cut a 6 month trip into 6 days, created jobs for many people and encouraged immigration. the homestead act played a huge role in western expansion; it allowed settlers to begin a fresh start, and gave them land in exchange for their residence for up to five years and a small fee.