Marco Has Noticed That as Older Adults Purchase Tablets, They

Marco has noticed that as older adults purchase tablets, they do not know much about how to use them and are frequently aggravated. He decided he could earn a nice profit by developing courses and offering one-on-one help to aid his customers in overcoming their deficiencies. Although the business struggled at first, he is experiencing a good deal of success now. Marco has many satisfied customers, and the business has grown to the point where he now employs several workers, some of whom were previous clients. Marco's experience is an example of

A) socialism at work.
B) the principle of comparative advantage.
C) the invisible hand concept.
D) the multiplier principle.