The correct answer is A.
It is a observational study because the researcher (the coach) observes the performance of a specific group of individuals (no randomization) in their natural state and environment, and with the information gathered he reaches a conclusion.
It is not an artificially created environment, with randomized subjects confronted to a specific prearranged situation to observe how their behave. Such a study would be an experiment.
It cannot be a double-blinded study because the coach knows about it in advance. It could be a blinded-study if the other side of the research, the swimers, did not know. This is not especified and, moreover, the blinded-study is not listed in the answers proposed.
