premise: St. Joseph's School is a historic former school building on Birch Street in Biddeford, Maine. Built in 1887, it was one of the first large masonry schools to be built in the state, and became a focal point for the migration of French Canadians into the state. It was listed on the National Register of Historic Places in 1983. It has been converted to residential use.
hypothesis: St. Joseph's School was listed on the National Register of Historic Places in the 20th century.
reason: It is stated that the St. Joseph's School was listed on the National Register of Historic Places in 1983. I stated the same but used the term "20th century" which is the same time period as 1983. I think the system got confused because of the "20" and it didn't know the full meaning of the term "20th century".