问题补充:
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
答案:
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。