There seems to be a clear relationship between the prevailing mortgage interest rates x and the number of new houses being built per month in a midwestern city y over a period of 18 months. A scatter plot of the data collected shows that the linear model is appropriate. The equation of the least-squares regression line is the number of new houses 672.89 - (30.65 x interest rate) and r² = 0.49. The association between the interest rate and the number of new houses
A. negative.
B. unknown.
C. positive.
D. zero.