Answer:
Observational study
Explanation:
In an experiment, one group is given a treatment and one group is a control group. There is only one group here; this is not an experiment.
A randomized trial involves some sort of random selection of participants; there is no randomization here, so this is not a randomized trial.
In a double-blind study, neither the participants nor the researcher are aware of the participants in the study; this is not a double-blind study.
The coach observes the amount of time the members of the team can hold their breath. This is an observational study.