[1] Our house was once a stop on the
Underground Railroad. [2] It was common
for an enslaved person to stop there on their
way to the North. [3] The Underground
Railroad were a network of hiding places. [4]
The cellar beneath our house has a secret
door that was installed to trick slave catchers.
[5] Living in a piece of American history is
pretty interesting. Which sentence contains a subject-verb
agreement error?