Which statement gives two central ideas from the passage? A. Construction of the transcontinental railroad took many years, and the transcontinental railroad helped the Union Army win the Civil War. B. Construction of the transcontinental railroad was very challenging, and the transcontinental railroad was important to the growth of the United States. C. Construction of the transcontinental railroad was very dangerous, and the transcontinental railroad made the United States a more diverse nation. D. Construction of the transcontinental railroad led to the invention of track ballast, and the transcontinental railroad helped Utah become a state