The market price of pizzas in a college town decreased recently, and the students in an economics class are debating the cause of the price decrease. some students suggest that the price decreased because a new type of pizza oven allows pizza shops to create a pizza in half the time. other students attribute the decrease in the price of pizzas to a recent increase in the price of beer. everyone agrees that the increase in the price of beer was caused by a recent increase in the price of grain, which is not generally used in making pizzas.

When cell phones were first entering the market, they were relatively large and reception was undependable. all cell phones were essentially the same. but as the technology developed, many competitors entered, introducing features unique to their phones. today, cell phones are only a small fraction of the size and weight of their predecessors. consumers can buy cell phones with color screens, cameras, internet access, daily planners, or voice activation (and any combination of these features). the history of the cell phone demonstrates what marketing trend?