单选题 He became a famous writer when he was ______ .
A. in his fifty B. in his fifties C. in fifty years old

【正确答案】 B

【答案解析】[解析] in one's fifties表示“(某人)五十多岁时”：在表示“几十多岁时”，用逢十的基数词的复数形式。