问题如下：
The following histogram shows a distribution of the S&P 500 Index annual returns from 1964 to 2013: 
Based on the previous histogram, the distribution is best described as having:
选项：
A. one mode.
B. two modes.
C. three modes
解释：
C is correct.
The mode of a distribution with data grouped in intervals is the interval with the highest frequency. The three intervals of 3% to 8%, 18% to 23%, and 28% to 33% all have a high frequency of 7
老师，好： 请教一下，3个interval区间frequency都是7，那么比如3-8这个区间，里面的分布如果是4个4%，3个5%。其他两个人区间也是同样情况。那么我们怎么确定众数？这题问法是不是有问题？谢谢