Answer:
D.
Explanation:
The Underground Railroad was the system through which many slaves were transported to the North and Canada. The term underground railroad was used as a code to confuse those trying to catch the slaves and their owners.
The other code word used was 'stationmasters.' The term referred to those who gave shelter to slaves in their house. And, the place where slaves rested was termed 'stations' or 'depots.'
The stationmasters were most likely abolitionists, who oppose the slavery. Some prominent abolitionists who sheltered slaves include Thomas Garett, Levi Coffin (also called the 'President of the Underground Railroad), Frederick Douglass, etc.
Therefore, option D is correct.
The correct answer would be to improved roads and rails networks.
