Why does learning remain merely individual in the absence of a human teacher?

Because each child studies separately with a machine

The governing concept is the difference between individualized machine instruction and collective classroom learning. In Margie's time, each child studies separately with a mechanical teacher in a private space. The machine presents lessons and records performance, but it does not bring children together for conversation, cooperation, comparison of ideas, or mutual encouragement. Therefore option A is correct: learning remains individual because every child works alone with a personal machine. Option B is irrelevant to classroom organization, C makes an unsupported claim about history, and D mistakes the County Inspector's technical inspection for the regular social role of a teacher. The point is isolation, not the difficulty of the subject.

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