Approximately what number of Americans over the age of 12 have tried marijuana at least once

A major problem with genetic explanations of racial differences in IQ is that:

a. although intelligence differs between groups, it does not differ within groups. b. heritability estimates used in supporting genetic explanations of group differences are based mainly on white samples. c. the studies typically use black and white children from highly similar socioeconomic groups. d. the explanations are based on linkage studies.

In Smith's feature comparison model, what is the difference between Stage I and Stage II comparisons of two concepts?

a) Stage II has less overlap of feature sets than Stage I b) Stage II is faster than Stage I. c) Stage II comparisons are false, while Stage I comparisons are true. d) Stage II relationships are more obvious than Stage I relationships.