He began to work there （ ）.A.on his fifty B.at the age of fi

A、on his fifty 应该是in his fifties 介词复数错误,意思：在五十几岁的时候、B、at the age of fifty 译为“在他五十岁时”,强调在他50岁那一年发生的事情C、when he fifty 本打算用时间状语从句,但是语法错误,应改为“when he was fifty”D、in his fifties 在他五十几岁的时候