To determine if the relationship is proportional, we need to check if the ratio of calories burned to time walking is constant for all given data points.
Here are the calculations for each pair of time and calories:
-
For 20 minutes:
- \( \frac{100 \text{ calories}}{20 \text{ minutes}} = 5 \text{ calories per minute} \)
-
For 30 minutes:
- \( \frac{150 \text{ calories}}{30 \text{ minutes}} = 5 \text{ calories per minute} \)
-
For 40 minutes:
- \( \frac{200 \text{ calories}}{40 \text{ minutes}} = 5 \text{ calories per minute} \)
-
For 60 minutes:
- \( \frac{300 \text{ calories}}{60 \text{ minutes}} = 5 \text{ calories per minute} \)
-
For 80 minutes:
- \( \frac{400 \text{ calories}}{80 \text{ minutes}} = 5 \text{ calories per minute} \)
Since the ratio of calories burned to time walking is constant at \(5\) for all data points, the relationship is proportional.
Therefore, the answer is: C. The relationship is proportional.