When I entered the room I found a little boy on his mother’s knees to draw a picture.A.

问题补充：

When I entered the room, I found a little boy on his mother’s knees to draw a picture.

A. seated; learning

B. sitting; to learn

C. seating; learning

D. sat; was learning

答案：

(答案→)A. seated; learning

B. sitting; to learn

C. seating; learning

D. sat; was learning

解析：seat是及物动词，后没有宾语， 故此处用过去分词做后置定语 表示“坐在……”a little boy 是learn的执行者所以用learning。