The population of a town is divided into three age categories. A random sample of each category is surveyed about voting
choices. This type of sampling is called
cluster sampling.
stratified sampling.
simple random sampling.
systematic random sampling.

stratified sampling

Explanation:

Stratified random sampling is a method of sampling in which a population is divided into smaller groups based on characteristics like male and female or education level to complete the sampling process. These smaller groups are known as strata. Under stratified sampling, the sample size required to achieve a given precision can be reduced.

this null effect is caused by a weak manipulation and ineffective internal validity. in a scientific study, as the one dr. morimoto is trying to perfom, internal validity refers to the confidence placed in the cause-effect relationship and to how well an experiment is done and able to eliminate confounding variables.        

what's this it's not giving you what have to do.