"Between 1864 and 1896, ten western territories became states" is the best example that states the positive effect of railroads on settlement in the west.
Option: D
Step-by-step explanation:
Establishment of first transcontinental railroad took place in 1869 which resulted from series of events. This development lead to expansion of west settlement as travelling was no more hurdle and population was no more biased. So they decided that land in west must be part of United States. Therefore when civil war was cooled down, in late 1880's and 1890's many former territories became states like North Dakota, South Dakota, Montana, Washington, Idaho, Wyoming, Utah, Colorado, Nevada. These were initiated to follow union and acquire statehood. While railroad had huge positive effect on economy as it enhanced the trade between east and west of USA which ultimately lead development of states too.