Final answer:
Coach Ferguson uses a thermometer to check the water temperature in Cool Pool.
Step-by-step explanation:
In the given scenario, Coach Ferguson uses a thermometer to check the water temperature in Cool Pool.
Thermometers are devices used to measure temperature. They can use different materials like mercury or alcohol that expand or contract with temperature changes.
By measuring the water temperature with a thermometer, Coach Ferguson can ensure that the pool is at the desired temperature for the players' comfort and safety.