Then professor walked onto the platform and seated himself in a chair for answering ques

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。