Suppose we calculate the least-squares regression lines for two sets of paired data. the first set has a regression line with slope m1 and correlation coefficient r1, while the second set has a regression line with slope m2 and correlation coefficient r2. if r1 < 0 < r2, we can correctly conclude that
a) m1 < 0 < m2
b) r1^2 < 0 < r2^2
c) the first set displays stronger correlation than the second.
d) the second set displays stronger correlation than the first.