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

he movement of air through earth's or any planet's atmosphere is called wind, and the main cause of earth's winds is uneven heating by the sun. this uneven heating causes changes of atmospheric pressure, and winds blow from regions with high pressure to those with low pressure.

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