The British refused and made an official declaration of war against Spain. On June 21, Spain responded by declaring war against Great Britain. The British made plans to attack New Orleans, the seat of government for the Spanish Colony of Louisiana. ... Galvez was made commander of all Spanish troops in North America.
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.
the widely used measure that he applied to his experiment was the benton facial recognition test. it employed on to football players and as result, only players who suffered brain concussions did not pas this test. and although it has an external validity, it is limited because it isn't general to apply to other population.
i would say b. research typically uses a variety of sources