Which of these is the best example of specialization?

Which of these is the best example of specialization?

Kaylee owns a gas station and is responsible for stocking the shelves as well as selling the products to customers.

Paul works at a car factory and is responsible for putting the wheels on every car.

Richard owns a cupcake shop and is responsible for preparing the ingredients, baking the cupcakes, and selling the desserts.

Jennie works at a furniture store and puts together all the furniture by herself.