Respuesta :
The answer is D Once the nuclear reactions stop, the star's center begins to cool.
The sentence from "Black Hole Beginnings" which underlines the effect is:
"Once the nuclear reactions stop, the star's center begins to cool." (Option D)
What is the article Black Hole Beginnings about?
The article speaks about the formation of stars in connection with nuclear reactions. It also speaks to the formation of black holes.
Hence the correct answer is Option D.
Learn more about Black Hole Beginnings at;
https://brainly.com/question/15456088