What business philosophy did ray kroc most likely follow?

Ray Kroc was born in Oak Park, Illinois, on October 5, 1902. He was of Austria-Hungarian origin and spent most of his childhood in Oak Park. At the age of 15, Ray lied about his age to become a Red Cross ambulance driver during the First World War. After which he tried his hand at various other jobs between 1918 and early 1950s. These includes paper cup salesman, pianist, jazz musician and a local DJ at Oak Park radio station. Eventually he became a sales person for a multi-mixer milkshake machine and started traveling around the country. It was during this time when he met the MacDonald brothers (Richard and Maurice MacDonald) who owned a then small restaurant fast food chain called MacDonald’s. Ray was surprised at the effectiveness of their operation. They produced a limited menu, concentrating on just a few items-burgers, fries and beverages-which allowed them to focus on quality at every step.

D. cooperation is the key to successful business