To understand this, let's think about what a box plot is.
The line in the middle is the median, or the 50% line.
The box is the IQR, and the ends of the box are the first quartile (Q1) and the third (Q3). 50% of the data is in the box.
The endpoints are the largest and smallest data values that aren't outliers (and it looks like there are no outliers, because I don't see any dots or stars on the outside of the plot).
Why not A: That's the median, not the mean.
Why not B: The box tells us that exactly 50% of the data lies between 3 and 9. I wouldn't call that a "majority."
Why not C: The distance from 9 and 15 makes up 25% of the data, as does that between 1 and 3.
