问题补充：
Peter is busy at school, but he never forgets exercise every day.
A. work, doing
B. working, to do
C. work, to do
D. working, doing
答案：
A. work, doing
(答案→)B. working, to do
C. work, to do
D. working, doing
解析：句意：彼得在学校忙于工作，但是他每天都不会忘记锻炼身体。be busy doing sth 忙于做某事，forget to do sth忘记做某事，故选B
