China's large mountains and vast deserts served to A isolate it from its neighbors. B limit their natural resources. C make growing plentiful crops difficult. D encourage invasions.

C4 i’m pretty sure

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.