Answer:
Option D.
Step-by-step explanation:
When we have a graph with two axes, in the usual notation we use the horizontal axis as the independent variable (the one we can modify) and the vertical axis represents the dependent variable (the one that changes in response to the independent one).
In this case, we can see that in the horizontal axis we have the number of toppings (and this makes sense, because we can choose the number of toppings that we want) while on the vertical axis we have the price (also makes sense, because the price depends on the number of toppings we want)
Then we can conclude that the independent variable is the number of toppings.
The correct option is D.
