What had replaced the human teacher in Margie's education?

Correct answer: The mechanical teacher

A mechanical teacher had replaced the human teacher in Margie’s education. It was a teaching machine installed in her home, and it displayed lessons, asked questions, and gave exercises through its screen. Margie normally studied alone under its supervision instead of attending a classroom led by a person. The story uses this arrangement to show how technology has changed education and removed direct daily contact with human teachers. Therefore, option A is correct. The old school was only something Margie read about, not her place of study; a playground cannot teach lessons; and a paper book is a source of reading, not a replacement for a teacher. These distinctions make the answer definite.