Then professor walked onto the platform and seated himself in a chair, for answering questions.
A. had prepared
B. being prepared
C. preparing
D. prepared
网友回答
A. had prepared
B. being prepared
C. preparing
(答案→)D. prepared
解析：句意：教授走上讲台，坐在椅子上，准备回答问题，这里使用了be prepared for…为…做好了准备，用过去分词做状语，所以选D。