12 Two quantities, x and y are measured on each of a group of
subjects. The correlation between these measurements is
denoted by r, and the least squares regression line of y on x is
given by y=ax+b. Pick out the one correct statement:
A. If r > 0, then a > 0
B. If b > 0, then r > 0
C. If a and b have different signs (i.e. one is positive, the
other negative), then r < 0.
D. Multiplying all the x and y values by the same positive
constant leaves both the regression line and the
correlation unchanged.