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

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A. to prepare
B. was preparing
C. prepared
(答案→)D. preparing
解析：考查现在分词做状语：句意：秘书忙到深夜给总统准备一篇很长的演讲稿。这里是伴随状语，因为The secretary和prepare是主动关系，用现在分词做状语，如果没有逗号,这里可以用to prepare,B是谓语动词，选D。