In "I saw a thief stealing something", the italicized part is
【正确答案】 C
【答案解析】现在分词用法题。see sb.do/doing sth.是“谓语+宾语+宾语补足语”结构,stealingsomething在这里作宾语补足语,对宾语a thief做补充说明,答案为C。