问题补充：
The secretary worked late into the night, a long speech for the president.
A. to prepare
B. prepared
C. preparing
D. to be prepared
答案：
A. to prepare
B. prepared
(答案→)C. preparing
D. to be prepared
解析：句意：秘书工作到很晚，为总统准备一个很长的演讲。这里需要非谓语动词做状语，因为the secretary和prepare是主动关系，用现在分词做状语，所以选C。
