What are the two variables that are incorporated in the hertzsprung-russell diagram?

a. a star's luminosity (brightness) and its surface temperature
b. a star's age and its surface temperature
c. a star's age and its distance from earth
d. a star's luminosity (brightness) and its distance from earth

Abeaker of water was heated and then placed on a bench in the laboratory. the water cooled until it was the same temperature as the air in the laboratory. which of these explains the mechanism by which the water cooled? a. heat energy was transferred from the water to the air. b. water molecules from the water formed warm water currents. c. the water molecules absorbed energy from the molecules in the air. d. the water released radiation until it contained no heat energy.