Final answer:
The best word to complete the sentence is 'excitement,' since the context indicates that the girl is experiencing a positive and eager reaction to seeing herself in the dress. Option d is the correct answer.
Step-by-step explanation:
The word that best completes the sentence 'The young girl looked at her mother with excitement when she saw the red dress in the store window' is excitement.
In the context provided, the girl is being fitted with a dress that has an apricot color which she evidently likes, as indicated by her being 'entranced' and 'surveying herself naively in the tall looking-glass.' These descriptions evoke a positive emotional reaction, one that reflects pleasure and eager interest, not contempt, disdain, or confusion.
The correct answer is D, excitement, as the context suggests she is likely thrilled to see herself in such a lovely dress, which is congruent with the positive emotional state implied by the descriptive text.