TOEFL Listening: TPO-TOEFL阅读TPO - _Y5C5164QTO43CLZN$

Why is "gravitational contraction" mentioned in the passage? A. To show that questions about the Sun's energy source were as interesting to early scientists as questions about Earth's age. B. To provide evidence that Hutton's ideas led to advances in physics and astronomy as well as in geology. C. To explain why there is such a tremendous amount of energy flowing from the Sun. D. To cite a method for estimating the age of the Sun that was used to determine Earth's age.