Once _____ of the necessity of a move, he worked hard to find a

Once _____ of the necessity of a move, he worked hard to find a new home.
A、convinced
B、be convinced
C、convincing
D、having convinced
【正确答案】：A
【题目解析】：be convinced of 相信，确信；once引导分词短语作状语，省略了be动词。