ANSWER:
Simple Random Sampling
Explanation:
The first thing is to know each type of sampling, like this:
Simple Random Sampling:
Each subject has an equal probability of being selected for the study.
Systematic Random Sampling:
All individuals on the list are taken and each 3, each 7, or any other number is selected.
Stratified sampling:
When the sample includes representative subgroups (strata) of the study elements with specific characteristics: urban, rural, educational level, academic year, career, sex, ethnic group, age, parity, etc.
Convenience sampling:
It is the sample that is available in the time or period of investigation.
According to these definitions we can affirm that the study carried out in the statement is a Simple Random Sampling.