Why is Margie's experience reliable for explaining the difference between a human teacher and a machine?

Because she herself is dissatisfied with machine-based lonely education

The governing concept is first-hand evidence. Margie personally studies through a mechanical teacher, becomes frustrated by its rigid lessons, and then discovers the description of old schools with human teachers and groups of children. Her reaction is therefore a direct emotional and practical comparison, not an opinion based on distant information. Option D is correct because her dissatisfaction and curiosity reveal what the machine cannot provide: companionship, flexible explanation, and a lively social setting. Options A, B, and C are factually unsupported; Margie is a schoolchild, not an old teacher, a teacher in every school, or a machine designer. Her experience makes the contrast convincing.

This is a Class 9 English question. Chapter: The Fun They Had. Topic: the importance of human teachers.