:3. A factory has 20 machines producing a product.  Usually
there are a number of machines which are out of order.  Let r be
the correlation coefficient between the number of machines which
are out of order and the number which are working.  Then <p>

a.  r is smaller than 0 but bigger than -1 <p>

b.  r = -1 <p>

c.  can't tell what r is <p>

d.  r is greater than or equal to 0, but less than 1 <p>

e.  r = 1 <p>