Answer:
Cohort study
Explanation:
A cohort study is a longitudinal studio (which mean a group is observed through time) where the sample is a cohort (people who share some characteristics) and they are used to identify factors that might contribute to a particular condition, illness or disease.
In this case, the sample was made of people who shared a common characteristic: being volleyball players. This study was used to identify how the use of sunscreen would affect the skin in terms of damage.
Therefore, we can say that this is an example of cohort study.