The individual pieces of info by themselves are of no use.

But combining both the pieces, we can arrive at the answer.

The line will be as shown in the diagram. Since the line passes through the origin and the slope is negative, the line has to be as shown, passing through the 2nd or the 4th quadrant.

Now point (a,b) could be in either quadrants (and hence in the diagram I have shown it as such).
But since its given that a < b, that is possible in the 2nd quadrant only (b is positive and a negative).

Hence C)

-A