In the mid 1800s, the specific network of route and safe house use by people ecaping slavery was know as

underground railroad

Explanation:

The Underground Railroad.

Explanation:

It was well-known -- well, as well known as it can be since it's was sort of a secret -- throughout the African-American slaves in the 19th century. The Underground Railroad was used as a means to escape from slavery in the South into free states and Canada.

f high

explanation:

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.