<span>Railroads created time zones, the growth of cities and the first truly national market.</span>
Dangerous. Poor ventilation, little to no health and safety measures, dusty, hot.
They were all slave states that had remained in the Union and this is what Missouri, Kentucky, Maryland and Delaware had in common during the Civil war. The correct option among all the options that are given in the question is the second option. I hope that this is the answer you were looking for and it helped you.
Because of racial oppression.