At the Time the Hypothesis Was Suggested, What Major Problem

At the time the hypothesis was suggested, what major problem was identified with the idea that the Sun was powered by gravitational contraction?

A) This process could not possibly lead to the observed power output of the Sun.
B) Contracting objects cool down rather than heat up.
C) 19th century astronomers should have been able to measure the required change in the Sun's size.
D) This process would power the Sun for only about 25 million years, but geologists already had evidence the Earth was much older than that.