If you want to assess presidential candidate preferences of maricopa county registered voters classified by social class and age, you might randomly select voters from each subgroup according to their proportion in the entire county. this sampling technique is called sampling

Stratified random sampling

Explanation:

In stratified random sampling the population of choice is partitioned into subgroups. Then the samples for study are selected randomly from the subgroups.  

The given situation is the example of stratified random sampling this is because of the fact that the population is divided into subgroups on the basis of the social class and age. Then the voters were randomly selected from each subgroup.

La Organización de las Naciones Unidas es una agrupación de países fundada en 1945 al finalizar la Segunda Guerra Mundial por 51 países. Su importancia es la de mantener la paz y la seguridad a nivel internacional y, sobre todo, promover entre las poblaciones las relaciones de amistad y progreso social, la mejora del nivel de vida y los derechos humanos.