Answer:
Ummm?
Explanation:
So this question doesn't seem to be complete since there isn't any answers to choose from but my guess that the author thinks the underground railroad was really cool or served many helpful purposes or something like that. It wouldn't be something negative so whichever one fits most into context.
<u><em>Subject. A subject in grammar is the first part in a sentence about which the second part, the predicate, tells something.</em></u>