When a change in the dependent variable could be due to an event beyond the researcher's control, _________ is a threat to internal validity

The percentage of Americans engaged in agricultural production today is about __________

a. 1 percent b. 4 percent c. 19 percent d. 23 percent

Mexico's Gini index score is about twice as high as Denmark's. Which statement best explains what this means?

a. Mexico has a standard of living that is roughly twice as high as that in Denmark. b. Mexico has a much larger gap between the rich and the poor than that in Denmark. c. There is far more government intervention in the economy in Mexico than in Denmark. d. The average productivity of workers in Mexico is roughly half that of workers in Denmark.