The sentence that best shapes the theme of the passage is:
B. (This, I thought, was reversing the order of things.)
This sentence reflects the central idea of the passage, highlighting the tension between the responsibilities of a caregiver (Miss Grey) and the unruly behavior of the children she is meant to supervise. It emphasizes the challenges of authority and the reversal of expected roles, which ties into themes of control, responsibility, and the difficulties of teaching.