An experimental researcher selects students who had low scores on a math pre-test and high scores on a math post-test to participate in a study examining the influence of a new math curriculum in an elementary school grade. What potential threat to validity exists in the experiment?

Which best describes the idea behind the "invisible hand"? producers decide what to make for consumers, which guides the economy. individuals seeking their own self interest benefit the economy as a whole. government sets policy for producers and consumers, which guides the economy. consumers decide what they need and want to buy, which guides the economy.

Why did separate government develop in ancient greece?

Push-and-pull factors contribute to