Concept:Emphatic stress on a word highlights the contrast with another option in the question.Explanation:The given sentence stresses BIG.This stress shows that the key contrast is between big and small.So the sentence is an answer to a question asking whether she slept on the small bed.The correct question must contain the opposite word "small" while keeping the rest identical.Among the options, only "Did she sleep on the small bed?" matches this contrast.Answer:B. Did she sleep on the small bed?