Because of technology, which feature of old schools had disappeared in the story?

Correct answer: Children studying together in a classroom

The governing idea is that technology has made schooling individual and home-based, but it has removed the shared classroom experience. In the future described by the story, each child studies separately with a mechanical teacher installed at home. When Margie reads about old schools, she learns that children once went to a special building, sat together, and learned from a human teacher. Therefore, option A is correct. The machine still checks answers and gives lessons, so B and C have not disappeared. Option D is unrelated because Margie still has a room for study at home.