The researchers studied the diets of thirty-one thousand children ages two to eighteen over a thirty-year period.

VOA: special.2010.03.17

Over that eighty-one year period you would have gotten a multiple of seventy-two.

经过81年时间,你翻了72倍

耶鲁公开课 - 金融市场课程节选

They had six children over a seven-year period, four girls and two boys.

VOA: special.2010.04.18