At one time—perhaps 30 or 40 years ago a manager could expect hi

At one time—perhaps 30 or 40 years ago a manager could expect his workers to stand up and give him a courteous greeting.
【正确答案】：ago—
【题目解析】：破折号可以用来分隔非限定性修饰语、同位语或附加说明的词语。