The demand for airline pilots depends on the demand for air travel.
Option C.
Step-by-step explanation:
The factors of a product are the combination of the resources and the materials which are used to produce a particular product in a particular quantity.
The demand of the product directly has a direct effect on the demand of the factor which is used to produce that particular product. With the increase in the demand of the product, the demand of the factor used to produce that particular product will also increase.