Which describes the territory of the Louisiana Purchase? (Select all that apply.)
1.The Louisiana Purchase doubled the size of the United States.
2.The Louisiana Purchase became all or part of 15 states,
3.The Louisiana Purchase stretched north into Canada.
4.The Louisiana Purchase stretched east from the Mississippi River to the Atlantic Ocean.

Dr. laguardia is a cognitive neuroscientist who is interested in the effect of brain concussions on the ability to recognize faces. he conducts a quasi-experimental study in which he examines football players before and after the regular season using the benton facial recognition test (a published, widely used measure of one's ability to recognize faces) to compare those who received concussions to those who did not. he finds that players who had concussions during the regular season performed worse on the benton facial recognition test than did players who did not experience which of the following is true regarding external validity in dr.laguardia's study? a. because dr. laguardia selected participants who actually experienced concussions, the study b. because dr. laguardia's study is a quasi-experiment, it is impossible to obtain c. because dr. laguardia's dependent variable was assessed in the laboratory, the study d. because dr. laguardia selected a widely used measure, his study generalizes to has strong external validity. external validity has limited external validity. other applications of this measure.