You are presented with the quiz "What is the initial cause of black holes?" But you don't know the answer, so you turn to your teacher to ask for hints. He says that "ablack hole is formed by a high-mass star collapses" and "then, gravity collapses the star". So, what's the best answer to the question?
Available choices:
a). energy
b). gravity
c). heat
d). photons
e). mechanical
f). sun's heat
g). cracking
h). Smoking
b).