Why did farming and trade revive in the high middle ages?

Firms use marginal analysis to determine prices by a) changing prices in accordance with information from retailers. b) using comparisons with strong competitors to position prices accordingly. c) examining the effect on revenue of small changes to the price of one item. d) trying to minimize production costs by using better and more efficient methods.

Which theory of color vision most accurately describes the process of color vision at the level of the retina?

What information does a survey provide? a. an accurate description of the population surveyed b. whether there is a predictive relationship between two variables? c. whether there is a cause-and-effect relationship between two variables d. none