[1] Our house was once a stop on the Underground Railroad. [2] The conductor of the Underground Railroad, Harriet Tubman, was known for their bravery. [3] It was common for an enslaved person to stop there while traveling North. [4] The Underground Railroad was a network of hiding places.
Which sentence has a pronoun-antecedent agreement error?
sentence 1
sentence 2
sentence 3
sentence 4