the morning of June 27 they visited the Great Wall.A. InB. AtC. OnD. From

问题补充：

the morning of June 27, they visited the Great Wall.

A. In

B. At

C. On

D. From

答案：

A. In

B. At

(答案→)C. On

D. From

解析：在具体某一天的早、下午、晚前要用介词On。