Why does a solar nebula flatten into a disk instead of a sphere, even though the gravity of a nebula pulls in all directions?
A This flattening occurs because the initial shape of the nebula is already somewhat flat.
B This flattening is a natural consequence of collisions between particles in a spinning cloud.
C. This flattening occurs because of gravitational influences of nearby stars.
D. This flattening occurs because the temperature of the solar nebula decreased as it collapsed.