What was the clearest negative effect of the machine teacher?

Correct answer: Feeling of loneliness

The governing concept is the social cost of replacing a shared classroom with individual machine instruction. Margie receives lessons at home from a mechanical teacher, so she studies by herself instead of meeting other children in a classroom. This arrangement may be orderly and convenient, but it removes ordinary companionship, discussion and shared experiences. Option B is correct because loneliness is the clearest negative effect shown by the story. Option A states the opposite of what happens. Option C refers to the discovery of Tommy's printed book, not the main effect of the machine teacher, and D is incorrect because Margie does not actually return to an old school. The contrast helps readers question whether efficiency alone makes education complete.