If a person on Earth views the Moon in a waxing crescent phase, in what phase would Earth appear to a person on the Moon?

Waning gibbous.

Explanation:

The waning gibbous moon, is defined to occur when the Moon appears to be more than one-half but not fully illuminated by direct sunlight. Because the fraction of the Moon’s disk that is illuminated is decreasing, we consider the Moon to be “waning.” Each new lunar cycle is measured beginning at each new moon and the waning gibbous moon occurs when the Moon is more than one-half but less than three-fourths of the way around the sky (i.e., along its orbit) from new moon.

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.