— When did your uncle arrive in China?— He got to Guangzhou the morning of the 16th of Apr

问题补充：

— When did your uncle arrive in China?

— He got to Guangzhou the morning of the 16th of April.

A. in

B. at

C. on

D. for

答案：

A. in

B. at

(答案→)C. on

D. for

解析：句意：你的叔叔什么时候达到中国？他在4月16日的早上达到了广州。在具体的某一天早上，下午，晚上用介词on.故选C