The statement “we need gas to start a car” fulfills the condition of being necessary but not sufficient. You cannot start a car if there is no gas in its gas tank. This means that having gas is a necessary condition for starting a car. However, it is very possible to have gas in the car’s tank and yet be unable to start the car. Therefore, having gas is not sufficient for starting a car.
In order to start a car, you need many things. You need gas in the gas tank. You need to have a key that allows you to start the car. The car needs to have a starter and all the necessary pieces of its engine. Because all of these things are necessary, just having gas in the tank is not sufficient for starting the car.
Therefore, Option C is the correct answer to this question.