Fact 1: Ablack hole is formed by a high-mass star collapses. Fact 2: Then, gravity collapses the star. Given the two facts above, what is the initial cause of black holes?
pick from the following.
a). energy.
b). gravity.
c). heat.
d). photons.
e). mechanical.
f). sun's heat.
g). cracking.
h). Smoking.
b).