What kind of writing did the mechanical teacher check?

Correct answer: Punch code

The governing concept is the highly automated method of assessment used in the future setting of the story. Margie's mechanical teacher required her to put answers into a special form, and it checked the answers written in punch code. Hence, option B is correct. Punch code is connected with machine-readable responses, not ordinary handwriting or classroom discussion. Option A is too limited, while options C and D are invented forms that are not mentioned in the passage. This detail emphasizes the contrast between mechanical checking and the more personal explanations that a human teacher could provide in an old-style school.