问题补充:
The boy found a wallet on the ground and stopped .
A. picking it up
B. picking up it
C. to pick it up
D. to pick up it
答案:
A. picking it up
B. picking up it
(答案→)C. to pick it up
D. to pick up it
解析:stop to do sth 表示停下去做另一件事,同时,pick ···up为动词+adv的情况,如果其宾语为人称代词时,需位于二者之间,故选C