With respect to how economists study the economy, which of the following statements is most accurate? a) economists study the past, but they do not try to predict the future. b) economists use "rules of thumb" to predict the future. c) economists devise theories, collect data, and analyze the data to test the theories. d) economists use controlled experiments in much the same way that biologists and physicists do.

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?