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

Which sentence has a subject-verb agreement error?
sentence 1
sentence 2
sentence 3
sentence 4