Which accurately describes a chart developed 20 years after a historical event?

Assuming that this is referring to the same list of options that was posted before with this question, the correct response would be "secondary source," since this would be analyzing something in the past. 

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.