问题补充：
As a volunteer ,Guo Mingyi always help others who are in trouble .
A. is ;seen
B. is ; seen to
C. is ; see
D. is ;saw
答案：
A. is ;seen
(答案→)B. is ; seen to
C. is ; see
D. is ;saw
解析：此题考查固定结构see sb do sth表示看到某人经常做某事。变为被动语态时的句型结构为be seen to do sth。
