Concept:Emphatic stress is used to contrast one word with another word of the same class that is implied in the question.
Explanation:The given sentence is: She slept on the BIG bed.
The stress falls on the word "BIG".
This shows the speaker is correcting an idea that she slept on a different bed, especially the small bed.
The word "BIG" is contrasted with "small", not with "under", "he", or "couch".
Option A asks: Did she sleep on the small bed?
The natural emphatic reply to this question is: No, she slept on the BIG bed.
Options B, C, and D would require different stressed words, such as "she", "on", or "bed", to make the sentence fit.
Therefore, the correct response is the question in Option A.
Answer:A. Did she sleep on the small bed?