He looks so tired. What’s wrong?- Nothing serious. He just stayed up last night hi

问题补充：

--- He looks so tired. What’s wrong?

--- Nothing serious. He just stayed up last night, his papers.

A. to prepare

B. having prepared

C. prepared

D. preparing

答案：

A. to prepare

B. having prepared

C. prepared

(答案→)D. preparing

解析：整个句子已经有谓语动词，所以该空应该用非谓语动词，又因为He与prepare之间是主动关系或伴随状语，故排除C；选项A表目的或将来，但是前面不用加逗号，故排除A；选项B表示它的动作发生在谓语动词之前，显然是错误的，故排除A，所以选D