Final answer:
Observations are statements or descriptions based on what is directly seen, heard, or experienced. The statement 'Thomas must have been exhausted after his swim because he was panting very hard and lying down on the pool deck' is an example of an observation.
Step-by-step explanation:
Observations are statements or descriptions based on what is directly seen, heard, or experienced. Out of the provided options, the one that is an observation is:
OA. Thomas must have been exhausted after his swim because he was panting very hard and lying down on the pool deck.
In this statement, the observer directly sees Thomas panting hard and lying down, which leads to the conclusion that he must be exhausted after his swim.