To determine if the relationship is proportional, we need to check if the ratio of calories burned to time walking is constant.
Let's calculate the ratio of calories burned to time walking for each point in the table:
- For 20 minutes: \( \frac{100 \text{ calories}}{20 \text{ minutes}} = 5 \)
- For 30 minutes: \( \frac{150 \text{ calories}}{30 \text{ minutes}} = 5 \)
- For 40 minutes: \( \frac{200 \text{ calories}}{40 \text{ minutes}} = 5 \)
- For 60 minutes: \( \frac{300 \text{ calories}}{60 \text{ minutes}} = 5 \)
- For 80 minutes: \( \frac{400 \text{ calories}}{80 \text{ minutes}} = 5 \)
Since the ratio of calories burned to time walking is constant (5 calories per minute), the relationship is proportional.
Therefore, the correct response is: The relationship is proportional.