Al's refusal to try sushi because all fish should be cooked, "just like Americans do," is an example of ___________ ethnocentrism

It is impossible to select for study adults who are similar to each other in every aspect except age; for this reason, cross-sectional research can easily be distorted by ______

Fill in the blank with correct word

Question Tests of all literate American draftees in World War I indicated that intelligence peaks at age

14. 18. 30. 42.