A figure shows four graphs labeled A, B, C, and D, each with an x and y axis and 0 at the origin, and each showing a curve. Graph A shows a straight line with a negative slope having x and y intercepts. Graph B shows a straight line with a positive slope having a y intercept above origin. Graph C shows an increasing concave up curve initiating at the origin. Graph D shows a straight line with a unit slope.

A proportional relationship is characterized by a straight line passing through the origin (0,0) and having a constant ratio between the variables.

Based on your description:
- Graph A shows a straight line with a negative slope having x and y intercepts. This does not pass through the origin.
- Graph B shows a straight line with a positive slope having a y intercept above the origin. This also does not pass through the origin.
- Graph C shows an increasing concave up curve initiating at the origin. This suggests a nonlinear relationship, not proportional.
- Graph D shows a straight line with a unit slope. If it passes through the origin, it indicates a proportional relationship.

Thus, the graph that shows a proportional relationship is:

**D**.