The interquartile range (IQR) is defined as the difference between the first and third quartiles (Q3−Q1). What feature of the box-and-whisker plot does the IQR describe?
A. the median of the data set
B. the full length of the box-and-whisker plot
C. the length of the box of the box-and-whisker plot
D. the average length of the two whiskers of the box-and-whisker plot