The amendments of 1970 and 1977 gave the Environmental Protection Agency the power to set air quality standards and to ensure that those standards are achieved according to a timetable prescribed by the agency.

The only thing I can think of is The Clean Air Acts. Although I do not know if that is the answer you are looking for.

answer:

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.