To measure whether older people are calmer than younger people, a researcher gives 20-year-olds, 40-year-olds, and 60-year-olds a questionnaire. this research technique is called a(n):

The technique used is sampling. The process that you will do in random sampling is there will be a selection of a subset of randomised number of the members of the population of a study. The researcher will have to take a portion of a population and treat them as representative of that population. There are actually a lot or different kinds of sampling. These are the random sampling, systematic sampling, stratified sampling, convenient sampling and judgment sampling, quota sampling and snowball sampling. Since the data is taken from every member of the population, this is called census study. It is a common knowledge that the entire population is too much to cover by the researcher alone thus this is what the researchers do. They then carefully choose samples to represent the whole population for their study.

Ithink it's c selection but i don't really know.