Restaurant Fast Food Is Faster to Make and Cheaper to Buy

Restaurant fast food is faster to make and cheaper to buy than a similar meal prepared at home.Which of the following does NOT explain these facts?  

A)  The preparation of restaurant fast food is divided into many separate tasks. 
B)  The larger-scale production of food in a restaurant allows the introduction of more efficient machines. 
C)  Workers in a fast-food restaurant gain productivity at a task over time. 
D)  Workers are more productive when they are being paid.