问题如下：
Which of the following statements is most accurate?
选项：
A.The arithmetic mean is appropriate to estimate the average returns over multiple periods.
B.The geometric mean is appropriate for assessing past performance.
C.The geometric mean is always greater than or equal to arithmetic mean.
解释：
B is correct. For reporting historical returns,the geometric mean is more appropriate because it is the rate of growth or return we would have had to earn each year to match the actual,cumulative investment performance.
老师您好，请问讲义上有一句话“the arithmetic mean is the statistically best estimator of the next year's returns given only the three years of return outcomes",课程上何璇老师是讲过算术平均预测将来更靠谱，但是为何讲义上特意强调“ best estimator of the next year's return" 且只能是“only the three years". 求教。感谢！
