The secretary worked late into the night a long speech for the president.A. to prepareB.

问题补充：

The secretary worked late into the night, a long speech for the president.

A. to prepare

B. preparing

C. prepared

D. was preparing

答案：

A. to prepare

(答案→)B. preparing

C. prepared

D. was preparing

解析：现在分词作状语时，其逻辑主语必须和主句的主语保持一致，也就是说主句的主语是现在分词动作的执行者。现在分词作状语也可表示时间、原因、伴随情况、结果等。故选B。若句中逗号改为句号时，可选A作目的状语。