To determine the total price when purchasing two medium one-topping pizzas with the given incentive, we need to analyze the pricing information.
- The cost of one one-topping medium pizza is $7.99.
- The special deal offers 2 one-topping medium pizzas for $6.49 each.
Now, let's calculate the total cost of purchasing two pizzas at the special price:
\[ \text{Cost of 2 pizzas} = 2 \times 6.49 = 12.98 \]
Thus, the total price when purchasing two medium one-topping pizzas under the incentive is $12.98.
The correct answer is:
D. $12.98