Answer:
Adolescents who have characteristics similar to those of the sample.
Step-by-step explanation:
If you are conducting a study and you use a sub-population, which means you choose a certain sample with similar characteristics, the result of the study cannot be generalized to the entire population. For example, you use a sample of adolescent between 14 to 16 years, this means that the result from this study would be applied to only adolescents with the characteristics that were similar to those participants used for the study.