Which of the following statements is most accurate?

a. warm air sinks.

b. warm air is less dense than cold air.

c. warm air is denser than cold air.

d. warm air exerts more pressure on the land than cold air.

To test the responsiveness of the kidneys, scientists have designed an experiment tracking urine output of people during a normal day, while regulating the in-take of water by mouth. what would be an appropriate hypothesis for this experiment?