$.$ Shortly after World War II$,$ Sam Jackson developed an idea for a biodegradable lubricant that was superior to anything currently on the market. He was excited about his new idea and, he persuaded a number of his friends to help produce samples. While demand kept up with production at first, he soon found he had to hire a sales force to sell excess product to manufacturing companies in the area. He decided this was primarily because his company had several strong competitors that had recently come into the industry. This is a good example of behavior one would expect in the $\_\_\_\_\_\_\_\_\_\_$ era of U$.$S$.$ business history.

A$.$ Marketing concept

B$.$ Market orientation

C$.$ Production

D$.$ Sales

E$.$ Societal marketing concept