:6. Consider diagram ? on page ? of the test. It shows a
scatter diagram, its approximate regression line, and four
vertical line segments marked A,B,C, and D. Each of these line
segments represents an error (where by the "error" of a point is
meant its distance from the regression line).  One of these
errors is about the size of the rms error of th regression line. 
Which one?

 a.  A

 b.  B

 c.  C

 d.  D