Why is the Hertzsprung-Russell (H-R) diagram an important tool for astronomers? Select the best answer.

A: it helps them classify stars.

B: it helps them study the life cycle phases of stars.

C: both A and B

D: neither A nor B

Which type of stimulus do mechanoreceptors detect? sound pain heat light

Which statement is the best summary of the model? a-a series of aerobic and anaerobic reactions take place in cells b- the sun's energy moves through trophic levels in a food chain c-light energy is converted into stored chemical energy plants.d- food molecules are broken down in the cells if living things.

Which organ controls breathing? lungs alveoli heart diaphragm