The correct answer is D. A sharp increase in the price of gasoline.
Step-by-step explanation
The term "incentive" is used to refer to a stimulus that is offered to a person, company, or sector of society to promote a specific behavior. According to this definition, it concluded that the best incentive to increase the demand for fuel-efficient cars is by increasing the price of fuel because if people have a fuel-efficient car they will have to pay more for fuel to a higher price. On the other hand, if they buy a fuel-efficient car, your money spent on gas will be less. Therefore, the correct answer is D. A sharp increase in the price of gasoline.