When researchers wish to create a pool of persons that represent the entire population, a method called is used to create that pool?

It is called "sampling". 

Sampling is a procedure utilized as a part of measurable investigation in which a predetermined number of observations are taken from a bigger populace. The approach used to sample from a bigger populace relies upon the kind of examination being performed, however may incorporate simple random sampling or systematic sampling.

answer; fair labor and standard act;

c is the newer have a great day