The boy often gives a satisfactory answer to the teacher’s question just a minute.So he’s

问题补充：

The boy often gives a satisfactory answer to the teacher’s question， just a minute.

So he’s usually the teacher’s pet.

A. thought

B. having thought

C. and to think

D. thinking

答案：

A. thought

(答案→)B. having thought

C. and to think

D. thinking

解析：-ing形式短语作状语,且think(思考)表示的动作发生于give a satisfactory answer之前,故用having thought。