smc

Geometrically, $b$ is the y-intercept, and $m$ is the slope. Since $mb>0$, then either we have a positive y-intercept and a positive slope, or a negative y-intercept and a negative slope. Lines with a positive y-intercept and positive slope can go through quadrants I, II, and III. They cannot go through quadrant IV, because if you start at $(0,b)$ for a positve $b$, you can't go down into the fourth quadrant with a positive slope. Thus, point $C$ is a possible point. Lines with a negative y-intercept and negative slope can go through quadrants II, III, and IV. Thus, point $D$ is a possible point. Looking at the axes, any point on the y-axis is possible. Thus, $A$ and $B$ are both possible. However, points on the positive x-axis are inpossible to reach. If you start with a positive y-intercept, you must go up and to the right. If you start with a negative y-intercept, you must go down and to the right. Thus, $\boxed{(1997,0)}$ cannot be reached.