:4. A scatter diagram contains five points.  Four of them lie on
a straight line.  The fifth one does not lie on that line.  Let r
be the correlation coefficient of the scatter diagram.  One of
the following is true.  Which one? <p>

a.   Since 80% of the points lie on a straight line, r has to
     equal 0.8 or -0.8.  <p>

b.   r has to equal -1  <p>

c.   r has to equal 1  <p>

d.   r is either 1 or -1, but we can't tell which.  <p>

e.   r doesn't need to be 0.8 or -0.8, but it certainly is   
     neither 1 nor -1.  <p>