Analysis of test questions: This question examines the content of the prosperous times of Kaiyuan. "Rice is fat and white, and public and private granaries are rich" means that rice with good color and clean millet are full of granaries of government and large families. It reflects the social and economic prosperity of Emperor Xuanzong of the Tang Dynasty during the Kaiyuan period, which is called "the prosperous time of Kaiyuan" in history. Therefore, the answer is A.