Concept:The idiom "raised eyebrows" is used to express surprise or mild shock at something.Explanation:In the sentence, the principal reacts to the student's explanation by raising his eyebrows.Raised eyebrows are a common non-verbal sign of surprise or disbelief.This idiom does not necessarily imply that the principal was unhappy or that he rejected the explanation outright.It also does not mean that he considered or weighed the explanation carefully.Rather, the action suggests that the principal found the explanation unexpected or astonishing.Therefore, the most appropriate interpretation is that the principal was surprised by the student's explanation.Thus, option D is the best answer.Answer:D. was surprised by the explanation